Mobile communication system, transmitting station, receiving station, relay station, communication path determining method, and communication path determining program

ABSTRACT

A mobile communication system determines a communication path to implement fast communication by multihop connection. A mobile communication system includes a mobile station, at least one relay station, and a base station and implements packet transmission from the mobile station to the base station through a communication path with an intermediary of at least one relay station or through a communication path without an intermediary of a relay station. The mobile communication system is provided with a communication path determiner for determining a communication path with a largest communication speed or a communication path satisfying a required line quality, based on interference levels of respective signals received at a relay station constituting a communication path between the transmitting station and the receiving station, and at the base station.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 10/483,998, filed Jun. 8, 2004,which is the National Stage of PCT/JP03/06360 filed May 21, 2003, andclaims the benefit of priority under 35 U.S.C. §119 from Japanese PatentApplications Nos. 2003-116095, filed Apr. 21, 2003, and 2002-153048,filed May 27, 2002, the entire contents of each which are incorporatedby reference.

TECHNICAL FIELD

The present invention relates to a mobile communication system capableof performing communication by multihop connection, a transmittingstation, a receiving station, and a relay station constituting themobile communication system, and a communication path determining methodand a communication path determining program for determining acommunication path by multihop connection and, more particularly, tothose applied to communication based on CDMA or OFCDM to implementmultiple access through coding of signals of respective channels.

BACKGROUND ART

A known method for the mobile communication systems to implementcommunication is one using the single hop connection system ofperforming transmission of signals while establishing a direct radiolink between a mobile station, such as a cell phone or the like, and abase station thereof (e.g., cf. Japanese Patent Application Laid-OpenNo. 6-53872). In radio link design for such mobile communicationsystems, there exist three variable elements of communication speed,maximum transmission power, and cell radius in terms of securingrequired SIR (Signal to Interference Ratio: ratio of received signalpower to interference signal power). Namely, the cell radius increaseswith increasing maximum transmission power as the communication speed iskept constant; whereas the cell radius decreases with increasingcommunication speed as the maximum transmission power is kept constant.

Incidentally, it is recently common to transmit or receive movingpictures with cell phones as well, and there are increasing needs forfast communication.

However, there is an upper limit on the transmission power of terminalequipment and in the communication systems by the above single hopconnection method, therefore, the maximum communication speed waslimited by distance between the base station and the mobile station,which made it difficult for the mobile station distant from the basestation to perform fast communication.

It is, therefore, an object of the present invention to provide asolution to the above problem by applying the multihop connection methodand thereby provide a mobile communication system capable of determininga communication path to implement fast communication by multihopconnection, a transmitting station, a receiving station, and a relaystation constituting the mobile communication system, and acommunication path determining method and a communication pathdetermining program for determining a communication path by multihopconnection.

DISCLOSURE OF THE INVENTION

In order to achieve the above object, a mobile communication systemaccording to the present invention is a mobile communication systemcomprising a transmitting station, at least one relay station, and areceiving station and configured to implement packet transmission fromthe transmitting station to the receiving station through acommunication path with an intermediary of at least one relay station orthrough a communication path without an intermediary of a relay station,the mobile communication system comprising communication pathdetermining means for determining a communication path with a largestcommunication speed or a communication path satisfying a required linequality, based on interference levels of respective signals received ata relay station constituting a communication path between thetransmitting station and the receiving station, and at the receivingstation.

A communication path determining method according to the presentinvention is a communication path determining method applied to a mobilecommunication system comprising a transmitting station, at least onerelay station, and a receiving station and adapted to determine acommunication path between the transmitting station and the receivingstation, the communication path determining method comprising acommunication path determining step of determining a communication pathwith a largest communication speed or a communication path satisfying arequired line quality, based on interference levels of respectivesignals received at a relay station constituting a communication pathbetween the transmitting station and the receiving station, and at thereceiving station.

A communication path determining program according to the presentinvention is a communication path determining program applied to amobile communication system comprising a transmitting station, at leastone relay station, and a receiving station, for determining acommunication path with an intermediary of at least one relay station ora communication path without an intermediary of a relay station, thecommunication path determining program letting a computer execute acommunication path determining step of determining a communication pathwith a largest communication speed or a communication path satisfying arequired line quality, based on interference levels of respectivesignals received at a relay station constituting a communication pathbetween the transmitting station and the receiving station, and at thereceiving station.

In radio communication, since the error rate increases with decrease inenergy per bit, the required value of SIR becomes higher for fastcommunication. Namely, in the case where the propagation distance isshort and the interference level is low, received SIR becomes highenough to implement fast communication. Based on such knowledge, themobile communication system (communication path determining method)according to the present invention is so configured that, in determininga communication path by multihop connection or by single hop connection,it determines the communication path with the largest communicationspeed or the communication path satisfying the required line quality,based on the interference levels of the respective signals received at arelay station constituting a communication path and at the receivingstation, whereby it can achieve implementation of fast communication.The “interference levels of respective signals received at a relaystation constituting a communication path and at the receiving station”refer to totals of received signal levels except for signals necessaryfor the host station of interest, out of signals received at thereceiving station or the relay station from other stations. The“transmitting station” and “receiving station” may be a mobile stationand a base station in the ordinary mobile communication systems or maybe relay stations for relaying packet transmission from the mobilestation to the base station. For example, where packets are transmittedfrom the mobile station via relay station A and relay station B to thebase station, the communication path determining method according to thepresent invention can be applied to determining the communication pathfrom the relay station A to the base station, supposing the relaystation A is the transmitting station.

The communication path determining program according to the presentinvention, when executed by a computer, is able to determine thecommunication path with the largest communication speed or thecommunication path satisfying the required line quality in much the samemanner as the above communication path determining method does, andthereby achieve implementation of fast communication.

The above mobile communication system may be configured so that thecommunication path determining means further comprises: interstationcommunication speed determining means for determining an interstationcommunication speed between each pair of stations, based on interferencelevels at respective stations constituting a communication path; andcommunication speed determining means for determining a communicationspeed on each communication path from the transmitting station to thereceiving station on the basis of the interstation communication speedbetween each pair of stations determined by the interstationcommunication speed determining means; and so that the communicationpath determining means determines a communication path on the basis ofcommunication speeds of respective communication paths determined by thecommunication speed determining means.

The above communication path determining method may be configured sothat the communication path determining step comprises: an interstationcommunication speed determining step of determining an interstationcommunication speed between each pair of stations, based on interferencelevels at respective stations constituting a communication path; and acommunication speed determining step of determining a communicationspeed on each communication path from the transmitting station to thereceiving station on the basis of the interstation communication speedbetween each pair of stations determined by the interstationcommunication speed determining means; and so that the communicationpath determining step is to determine a communication path on the basisof communication speeds of respective communication paths determined inthe communication speed determining step.

The above communication path determining program may be configured sothat the communication path determining step comprises: an interstationcommunication speed determining step of determining an interstationcommunication speed between each pair of stations, based on interferencelevels at respective stations constituting a communication path; and acommunication speed determining step of determining a communicationspeed on each communication path from the transmitting station to thereceiving station on the basis of the interstation communication speedbetween each pair of stations determined in the interstationcommunication speed determining step; and so that the communication pathdetermining step is to determine a communication path on the basis ofcommunication speeds of respective communication paths determined in thecommunication speed determining step.

In this manner, the mobile communication system (communication pathdetermining method) is able to determine the interstation communicationspeed between adjacent stations on a communication path, based on theinterference levels at the respective stations constituting thecommunication path, and determine the communication speed between thetransmitting station and the receiving station on the basis of theinterstation communication speeds thus determined. This permits thecommunication path determining means (the communication path determiningstep) to determine the communication path with the maximum communicationspeed or the communication path satisfying the required line quality,based on the communication speeds between the transmitting station andthe receiving station on the respective communication paths.

The communication path determining program according to the presentinvention, when executed by the computer, is able to determine thecommunication speed between the transmitting station and the receivingstation on each communication path, based on the interstationcommunication speeds determined from the interference levels, anddetermine the communication path on the basis thereof in much the samemanner as the above communication path determining method does.

The above mobile communication system may be configured as follows: thetransmitting station comprises request signal transmitting means fortransmitting a request signal; the receiving station comprises requestresponse signal transmitting means for transmitting a request responsesignal to a request signal; the relay station comprises request signaltransmitting means for transmitting a request signal, and requestresponse signal transmitting means for transmitting a request responsesignal to a request signal; information about the interstationcommunication speed determined by the interstation communication speeddetermining means is put into a request signal or a request responsesignal to be transmitted to the transmitting station, the receivingstation, or the relay station having the communication path determiningmeans.

The above communication path determining method may be configured tocomprise a request signal transmitting step wherein the transmittingstation or the relay station transmits a request signal; and a requestresponse signal transmitting step wherein the receiving station or therelay station transmits a request response signal to a request signal;and configured so that information about the interstation communicationspeed determined in the interstation communication speed determiningstep is put into a request signal or a request response signal to betransmitted to the transmitting station, the receiving station, or therelay station to execute the communication path determining step.

In this manner the information about the interstation communicationspeed between each pair of stations is put into a request signal or arequest response signal to be transmitted to the station having thecommunication path determining means (or the station to execute thecommunication path determining step), whereby the communication speedbetween the transmitting station and the receiving station can bedetermined at the station that receives the information about theinterstation communication speed between each pair of stationsconstituting the communication path.

The above mobile communication system may be configured so that thereceiving station and the relay station comprise request signalreceiving means for receiving a request signal transmitted from thetransmitting station through a communication path with an intermediaryof at least one relay station or through a communication path without anintermediary of a relay station; interference level measuring means formeasuring an interference level at the host station when the requestsignal receiving means receives the request signal; and communicationpropriety determining means for determining whether it is possible toperform communication requested by the request signal, based on theinterference level measured by the interference level measuring means;and so that the communication path determining means determines thecommunication path on the basis of propriety of communication determinedby the communication propriety determining means.

The above communication path determining method may be configured tofurther comprise a request signal transmitting step wherein thetransmitting station transmits a request signal to request communicationat a predetermined communication speed, to the receiving station or therelay station through a communication path with an intermediary of atleast one relay station or through a communication path without anintermediary of a relay station; an interference level measuring stepwherein the receiving station or the relay station measures aninterference level at the receiving station when receiving the requestsignal; and a communication propriety determining step wherein thereceiving station or the relay station determines whether it is possibleto perform the communication requested by the request signal, based onthe interference level measured in the interference level measuringstep; and configured so that the communication path determining step isto determine the communication path on the basis of information aboutpropriety of communication determined in the communication proprietydetermining step.

In this manner the receiving station or the relay station has thecommunication propriety determining means (the communication proprietydetermining step) for determining whether it is possible to perform thecommunication with the transmitting station on the basis of the requestsignal and the interference level, and the receiving station or therelay station receiving a request signal determines whether it ispossible to perform the communication requested by the request signal.This permits the communication path determining means (the communicationpath determining step) to determine whether it is possible to performthe communication at the predetermined communication speed, based on theresult of the determination by the communication propriety determiningmeans (or in the communication propriety determining step), and todetermine the communication path.

The above mobile communication system may be configured so that thetransmitting station comprises the communication path determining meanshaving request signal transmitting means for transmitting a requestsignal to request communication at a predetermined communication speed;and request response signal receiving means for receiving a requestresponse signal to the request signal transmitted by the request signaltransmitting means; so that when that it is impossible to perform thecommunication at the predetermined communication speed is determinedbased on the communication propriety information included in the requestresponse signal received by the request response signal receiving means,the transmitting station transmits the request signal while stepwiselowering the request communication speed, before a determination ofbeing communicable is made; and so that when it is determined that it ispossible to perform the communication at the predetermined communicationspeed, the transmitting station starts the communication with thereceiving station at the communication speed determined as communicable.

In this manner, based on the communication propriety informationincluded in the request response signal, the communication is started atthe communication speed if it is possible to perform the communication,whereas if it is impossible to perform the communication, the requestsignal is transmitted while stepwise decreasing the requestcommunication speed, before a determination of being communicable ismade. This enables the communication at the largest communication speedavailable for communication between the transmitting station and thereceiving station.

The above mobile communication system may be configured so that thetransmitting station comprises the communication path determining meanshaving request signal transmitting means for transmitting a requestsignal to request communication at a predetermined communication speed;and request response signal receiving means for receiving a requestresponse signal to the request signal transmitted by the request signaltransmitting means; so that when that it is possible to perform thecommunication at the predetermined communication speed is determinedbased on the communication propriety information included in the requestresponse signal received by the request response signal receiving means,the transmitting station transmits the request signal while stepwiseincreasing the request communication speed, before a determination ofbeing uncommunicable is made; and so that when it is determined that itis impossible to perform the communication at the predeterminedcommunication speed, the transmitting station starts the communicationwith the receiving station at a maximum communication speed out ofcommunication speeds determined as communicable.

As described above, when it is possible to perform the communication,based on the communication propriety information included in the requestresponse signal, the transmitting station transmits the request signalwhile stepwise increasing the request communication speed, before adetermination of being uncommunicable is made, and, with a determinationof being uncommunicable, it starts the communication at the maximumcommunication speed out of communication speeds determined ascommunicable. This enables the communication at the maximumcommunication speed available for communication between the transmittingstation and the receiving station, and communication can be establishedat the communication speed first determined as communicable, which candecrease a period of time before the establishment of connection.

The above mobile communication system may be configured so that thereceiving station and the relay station comprise request signalreceiving means for receiving a request signal transmitted from thetransmitting station through a communication path with an intermediaryof at least one relay station or through a communication path without anintermediary of a relay station; interference level measuring means formeasuring an interference level at the host station when the requestsignal receiving means receives a request signal; communicationpropriety determining means for determining whether it is possible toperform communication at a communication speed included in the requestsignal, based on the interference level measured by the interferencelevel measuring means; and request response signal transmitting meansfor transmitting a request response signal containing information onpropriety of communication determined by the communication proprietydetermining means, through the communication path to the transmittingstation; so that the transmitting station comprises the communicationpath determining means having request signal transmitting means fortransmitting a request signal to request communication at apredetermined communication speed; and request response signal receivingmeans for receiving a request response signal to the request signaltransmitted by the request signal transmitting means; so that when thatit is impossible to perform the communication at the predeterminedcommunication speed is determined based on the communication proprietyinformation included in the request response signal received by therequest response signal receiving means, the transmitting stationtransmits the request signal while stepwise lowering the requestcommunication speed, before a determination of being communicable ismade; and so that when it is determined that it is possible to performthe communication at the predetermined communication speed, thetransmitting station starts the communication with the receiving stationat the communication speed determined as communicable.

The above communication path determining method may be configured tofurther comprise a request signal transmitting step wherein thetransmitting station transmits a request signal to request communicationat a predetermined communication speed, to the receiving station or therelay station through a communication path with an intermediary of atleast one relay station or through a communication path without anintermediary of a relay station; an interference level measuring stepwherein the receiving station or the relay station measures aninterference level at the receiving station or the relay station whenreceiving a request signal; a communication propriety determining stepwherein the receiving station or the relay station determines whether itis possible to perform communication at a communication speed includedin the request signal, based on the interference level measured in theinterference level measuring step; and a request response signaltransmitting step wherein the receiving station or the relay stationtransmits a request response signal containing information on proprietyof communication determined in the communication propriety determiningstep, to the transmitting station through a predetermined communicationpath; so that the communication path determining step is configured asfollows: when that it is impossible to perform the communication at thepredetermined communication speed is determined based on thecommunication propriety information included in the request responsesignal transmitted in the request response signal transmitting step, therequest signal is transmitted while stepwise decreasing the requestcommunication speed, before a determination of being communicable ismade; when it is determined that it is possible to perform thecommunication at the predetermined communication speed, thecommunication is started with the receiving station or the relay stationat the communication speed determined as communicable.

In this manner the receiving station and the relay station have thecommunication propriety determining means (communication proprietydetermining step) for determining whether it is possible to perform thecommunication with the transmitting station, on the basis of the requestsignal and the interference level, put the information about proprietyof communication thus determined, into the request response signal, andtransmit the request response signal; the communication path determiningmeans (communication path determining step) is thus able to determinewhether it is possible to perform the communication at the predeterminedcommunication speed. When the result of the determination is that it ispossible to perform the communication, the communication is initiated atthe communication speed; when it is impossible to perform thecommunication, the request signal is transmitted while stepwisedecreasing the request communication speed, before a determination ofbeing communicable is made. This enables the communication at themaximum communication speed available for communication between thetransmitting station and the receiving station.

The above mobile communication system may be configured so that thereceiving station and the relay station comprise request signalreceiving means for receiving a request signal transmitted from thetransmitting station through a communication path with an intermediaryof at least one relay station or through a communication path without anintermediary of a relay station; interference level measuring means formeasuring an interference level at the host station when the requestsignal receiving means receives a request signal; communicationpropriety determining means for determining whether it is possible toperform communication at a communication speed included in the requestsignal, based on the interference level measured by the interferencelevel measuring means; and request response signal transmitting meansfor transmitting a request response signal containing information onpropriety of communication determined by the communication proprietydetermining means, through the communication path to the transmittingstation; so that the transmitting station comprises the communicationpath determining means having request signal transmitting means fortransmitting a request signal to request communication at apredetermined communication speed; and request response signal receivingmeans for receiving a request response signal to the request signaltransmitted by the request signal transmitting means; so that when thatit is possible to perform the communication at the predeterminedcommunication speed is determined based on the communication proprietyinformation included in the request response signal received by therequest response signal receiving means, the transmitting stationtransmits the request signal while stepwise increasing the requestcommunication speed, before a determination of being uncommunicable ismade; and so that when it is determined that it is impossible to performthe communication at the predetermined communication speed, thetransmitting station starts the communication with the receiving stationat a maximum communication speed out of communication speeds determinedas communicable.

The above communication path determining method may be configured tofurther comprise a request signal transmitting step wherein thetransmitting station transmits a request signal to request communicationat a predetermined communication speed, to the receiving station or therelay station through a communication path with an intermediary of atleast one relay station or through a communication path without anintermediary of a relay station; an interference level measuring stepwherein the receiving station or the relay station measures aninterference level at the receiving station or the relay station whenreceiving a request signal; a communication propriety determining stepwherein the receiving station or the relay station determines whether itis possible to perform communication at a communication speed includedin the request signal, based on the interference level measured in theinterference level measuring step; and a request response signaltransmitting step wherein the receiving station or the relay stationtransmits a request response signal containing information on proprietyof communication determined in the communication propriety determiningstep, to the transmitting station through a predetermined communicationpath; so that the communication path determining step is configured asfollows: when that it is possible to perform the communication at thepredetermined communication speed is determined based on thecommunication propriety information included in the request responsesignal transmitted in the request response signal transmitting step, therequest signal is transmitted while stepwise increasing the requestcommunication speed, before a determination of being uncommunicable ismade; when it is determined that it is impossible to perform thecommunication at the predetermined communication speed, thecommunication is started with the receiving station or the relay stationat a maximum communication speed out of communication speeds determinedas communicable.

In this manner the receiving station or the relay station has thecommunication propriety determining means (communication proprietydetermining step) for determining whether it is possible to perform thecommunication with the transmitting station, on the basis of the requestsignal and the interference level, puts the information about thepropriety of communication thus determined, into the request responsesignal, and transmits the request response signal, whereby thecommunication path determining means (communication path determiningstep) is able to determine whether it is possible to perform thecommunication at the predetermined communication speed. When the resultof the determination is that it is possible to perform thecommunication, the request signal is transmitted while stepwiseincreasing the request communication speed, before a determination ofbeing uncommunicable is made; with a determination of beinguncommunicable, the communication is started at the maximumcommunication speed out of communication speeds determined ascommunicable. This enables the communication at the maximumcommunication speed available for communication between the transmittingstation and the receiving station, and communication can be establishedat the first communicable communication speed, which can decrease theperiod of time before the establishment of connection.

The mobile communication system may be configured so that the relaystation further comprises request signal transmitting means fortransmitting a request signal to the receiving station or another relaystation only when the communication propriety determining meansdetermines that it is possible to perform communication; and requestresponse signal receiving means for receiving a request response signalto the request signal transmitted by the request signal transmittingmeans.

The above communication path determining method may be configured tofurther comprise a second request signal transmitting step wherein therelay station transmits a request signal to the receiving station oranother relay station only when the communication propriety determiningstep results in determining that it is possible for the relay station toperform communication; and a second request response signal transmittingstep wherein the receiving station or other relay station as adestination of the request signal in the second request signaltransmitting step transmits a request response signal to the requestsignal.

Since in an uncommunicable state between certain stations constituting acommunication path it is impossible to perform communication through thecommunication path, the relay station is configured so that only whenthe communication propriety determining means (communication proprietydetermining step) determines that it is possible for the relay stationto perform communication, the request signal is further transmitted tosearch for a communication path to the receiving station and so thatwhen it determines that it is impossible to perform the communication,transmission of the request signal is stopped at that point and therequest response signal containing information about the incapability ofcommunication is transmitted; whereby the system is prevented fromtransmitting ineffectual request signals, which can achieve increase ofefficiency of the mobile communication system.

The above mobile communication system may be configured as follows: thereceiving station comprises request signal receiving means for receivinga request signal transmitted from the transmitting station or the relaystation; interference level measuring means for measuring aninterference level at the receiving station when the request signalreceiving means receives a request signal; and request response signaltransmitting means for transmitting a request response signal containingthe interference level measured by the interference level measuringmeans, to the transmitting station or the relay station as a source ofthe request signal; the relay station comprises request signal receivingmeans for receiving a request signal transmitted from the transmittingstation or another relay station; interference level measuring means formeasuring an interference level at the host relay station when therequest signal receiving means receives a request signal; request signaltransmitting means for transmitting a request signal; request responsesignal receiving means for receiving a request response signaltransmitted from the receiving station or a second other relay station,in response to the request signal transmitted by the request signaltransmitting means; interstation communication speed determining meansfor determining an interstation communication speed between the relaystation and the receiving station or the second other relay station as asource of the request response signal, based on an interference levelincluded in the request response signal received by the request responsesignal receiving means; and request response signal transmitting meansfor transmitting a request response signal containing the interferencelevel measured by the interference level measuring means, and theinterstation communication speed information determined by theinterstation communication speed determining means, and, where therequest response signal received by the request response signalreceiving means is one containing interstation communication speedinformation, also containing the interstation communication speedinformation, to the transmitting station or the other relay station as asource of the request signal; the transmitting station comprises thecommunication path determining means having request signal transmittingmeans for transmitting a request signal; request response signalreceiving means for receiving a request response signal to the requestsignal transmitted by the request signal transmitting means;interstation communication speed determining means for determining aninterstation communication speed between the transmitting station andthe receiving station or relay station as a source of the requestresponse signal, based on an interference level included in the requestresponse signal; communication speed determining means for determining acommunication speed on a communication path from the transmittingstation to the receiving station on the basis of the interstationcommunication speed determined by the interstation communication speeddetermining means, and, where the request response signal contains aninterstation communication speed, on the basis of the interstationcommunication speed information as well; and communication pathselecting means for selecting a communication path on the basis ofcommunication speeds on respective communication paths determined by thecommunication speed determining means.

The above communication path determining method may be configured tofurther comprise a request signal transmitting step wherein thetransmitting station transmits a request signal to the receiving stationor the relay station; a second request signal transmitting step whereinwhen the relay station receives a request signal, the relay stationtransmits a request signal to the receiving station or another relaystation; an interference level measuring step wherein the receivingstation or the relay station receiving the request signal transmitted inthe request signal transmitting step or in the second request signaltransmitting step measures an interference level at the receivingstation or the relay station; a request response signal transmittingstep wherein the receiving station or the relay station transmits arequest response signal containing the interference level measured inthe interference level measuring step, to the transmitting station orthe relay station as a source of the request signal; and an interstationcommunication speed determining step wherein the transmitting station orthe relay station determines an interstation communication speed betweenthe station and the receiving station or the relay station as a sourceof the request response signal, based on the interference level includedin the request response signal transmitted in the request responsesignal transmitting step; and configured as follows: the interstationcommunication speed information determined at the relay station in theinterstation communication speed determining step is put into a requestresponse signal transmitted in the request response signal transmittingstep to be transmitted via at least one relay station or directly to thetransmitting station; the communication path determining step comprisesa communication speed determining step wherein the transmitting stationdetermines a communication speed on each communication path between thetransmitting station and the receiving station, based on an interstationcommunication speed between each pair of stations on a communicationpath between the transmitting station and the receiving station; and acommunication path selecting step wherein a communication path isselected based on communication speeds on respective communication pathsdetermined in the communication speed determining step.

In the mobile communication system (communication path determiningmethod) according to the present invention, the receiving stationmeasures the interference level at the receiving station when receivinga request signal having been transmitted from the transmitting stationor the relay station, and transmits a request response signal containingthe measured interference level, to the transmitting station or therelay station as a source thereof, and the transmitting station or therelay station receiving the request response signal determines theinterstation communication speed between the station and the receivingstation as a source of the request response signal on the basis of theinterference level included in the request response signal. The relaystation measures the interference level at itself when receiving arequest signal having been transmitted from the transmitting station oranother relay station, and transmits a request response signalcontaining the measured interference level to the transmitting stationor the relay station as a source thereof, and the transmitting stationor the relay station receiving the request response signal determinesthe interstation communication speed between the station and thereceiving station or the relay station as a source of the requestresponse signal on the basis of the interference level included in therequest response signal. Then each relay station also puts theinterstation communication speed information about the determinedinterstation communication speed into the request response signal andtransmits the request response signal to the transmitting station. Thetransmitting station determines the interstation communication speedbetween the station and the receiving station or the relay station as asource of the request response signal, based on the interference levelincluded in the request response signal transmitted from the receivingstation or the relay station. This permits the transmitting station todetermine the total communication speed between the transmitting stationand the receiving station on the basis of the interstation communicationspeed between each pair of stations constituting a communication pathbetween the transmitting station and the receiving station and determinethe communication path with the highest communication speed or thecommunication path satisfying the required line quality on the basis ofthe communication speed.

The above mobile communication system may be configured as follows: thereceiving station comprises request signal receiving means for receivinga request signal transmitted from the transmitting station or the relaystation; interference level measuring means for measuring aninterference level at the receiving station when the request signalreceiving means receives a request signal; interstation communicationspeed determining means for determining an interstation communicationspeed between the receiving station and the transmitting station or therelay station as a source of the request signal, based on theinterference level measured by the interference level measuring means;and request response signal transmitting means for transmitting arequest response signal containing the interstation communication speedinformation determined by the interstation communication speeddetermining means, to the transmitting station or the relay station as asource of the request signal; the relay station comprises request signalreceiving means for receiving a request signal transmitted from thetransmitting station or another relay station; interference levelmeasuring means for measuring an interference level at the host relaystation when the request signal receiving means receives a requestsignal; interstation communication speed determining means fordetermining an interstation communication speed from the transmittingstation or the other relay station as a source of the request signal,based on the interference level measured by the interference levelmeasuring means; request signal transmitting means for transmitting arequest signal; request response signal receiving means for receiving arequest response signal transmitted from the receiving station or asecond other relay station, in response to the request signaltransmitted by the request signal transmitting means; and requestresponse signal transmitting means for transmitting a request responsesignal containing the interstation communication speed informationdetermined by the interstation communication speed determining means andthe interstation communication speed information included in the requestresponse signal received by the request response signal receiving means,to the transmitting station or the other relay station as a source ofthe request signal; the transmitting station comprises the communicationpath determining means having request signal transmitting means fortransmitting a request signal; request response signal receiving meansfor receiving a request response signal to the request signaltransmitted by the request signal transmitting means; communicationspeed determining means for determining a communication speed on eachcommunication path from the transmitting station to the receivingstation, based on the interstation communication speed informationincluded in the request response signal received by the request responsesignal receiving means; and communication path selecting means forselecting a communication path, based on communication speeds onrespective communication paths determined by the communication speeddetermining means.

The above communication path determining method may be configured tofurther comprise a request signal transmitting step wherein thetransmitting station transmits a request signal to the receiving stationor the relay station; a second request signal transmitting step whereinwhen the relay station receives a request signal, the relay stationtransmits a request signal to the receiving station or another relaystation; an interference level measuring step wherein the receivingstation or the relay station receiving the request signal transmitted inthe request signal transmitting step or in the second request signaltransmitting step measures an interference level at the receivingstation or the relay station; an interstation communication speeddetermining step wherein the receiving station or the relay stationdetermines an interstation communication speed between the station andthe transmitting station or the relay station as a source of the requestsignal, based on the interference level measured in the interferencelevel measuring step; and a request response signal transmitting stepwherein the receiving station or the relay station transmits a requestresponse signal containing the interstation communication speedinformation determined in the interstation communication speeddetermining step, to the transmitting station or the relay station as asource of the request signal; and configured as follows: theinterstation communication speed information determined at the receivingstation or the relay station in the interstation communication speeddetermining step is put into a request response signal transmitted inthe request response signal transmitting step and the request responsesignal is transmitted via at least one relay station or directly to thetransmitting station; the communication path determining step comprisesa communication speed determining step wherein the transmitting stationdetermines a communication speed on each communication path between thetransmitting station and the receiving station, based on theinterstation communication speed between each pair of stations on acommunication path between the transmitting station and the receivingstation; and a communication path selecting step wherein a communicationpath is selected based on communication speeds on respectivecommunication paths determined in the communication speed determiningstep.

In the mobile communication system (communication path determiningmethod) according to the present invention, the relay station measuresthe interference level at the relay station itself when receiving therequest signal having been transmitted from the transmitting station oranother relay station, and determines the interstation communicationspeed between the relay station and the transmitting station or theother relay station as a source of the request signal on the basis ofthe interference level thus measured. The receiving station measures theinterference level at itself when receiving the request signal havingbeen transmitted from the transmitting station or another relay station,and determines the interstation communication speed between thereceiving station and the transmitting station or the relay station as asource of the request signal on the basis of the measured interferencelevel. Then the receiving station and each relay station put theinterstation communication speed information about the determinedinterstation communication speed into a request response signal andtransmit the request response signal to the transmitting station. Thispermits the transmitting station to determine the total communicationspeed on each communication path between the transmitting station andthe receiving station on the basis of the interstation communicationspeed between each pair of stations constituting a communication pathbetween the transmitting station and the receiving station and todetermine the communication path with the highest communication speed orthe communication path satisfying the required line quality on the basisof the communication speed.

The above mobile communication system may be configured as follows: therelay station comprises request signal receiving means for receiving arequest signal transmitted from the transmitting station or anotherrelay station; interference level measuring means for measuring aninterference level at the host relay station when the request signalreceiving means receives a request signal; interstation communicationspeed determining means for determining an interstation communicationspeed between the relay station and the transmitting station or theother relay station as a source of the request signal, based on theinterference level measured by the interference level measuring means;and request signal transmitting means for transmitting a request signalcontaining the interstation communication speed information determinedby the interstation communication speed determining means and, where therequest signal is one containing interstation communication speedinformation, also containing the interstation communication speedinformation; the receiving station comprises the communication pathdetermining means having: request signal receiving means for receiving arequest signal transmitted from the transmitting station or the relaystation; interference level measuring means for measuring aninterference level at the receiving station when the request signalreceiving means receives a request signal; interstation communicationspeed determining means for determining an interstation communicationspeed between the receiving station and the transmitting station or therelay station as a source of the request signal, based on theinterference level measured by the interference level measuring means;communication speed determining means for determining a communicationspeed on each communication path between the transmitting station andthe receiving station, based on the interstation communication speeddetermined by the interstation communication speed determining meansand, where the request signal is one containing interstationcommunication speed information, also based on the interstationcommunication speed information; and communication path selecting meansfor selecting a communication path, based on communication speeds onrespective communication paths determined by the communication speeddetermining means.

The above communication path determining method may be configured tofurther comprise a request signal transmitting step wherein thetransmitting station transmits a request signal to the receiving stationor the relay station; a second request signal transmitting step whereinwhen the relay station receives a request signal, the relay stationtransmits a request signal to the receiving station or another relaystation; an interference level measuring step wherein the receivingstation or the relay station receiving the request signal transmitted inthe request signal transmitting step or in the second request signaltransmitting step measures an interference level at the receivingstation or the relay station; and an interstation communication speeddetermining step wherein the receiving station or the relay stationdetermines an interstation communication speed between the station andthe transmitting station or the relay station as a source of the requestsignal, based on the interference level measured in the interferencelevel measuring step; and configured as follows: the interstationcommunication speed information determined at the relay station in thesecond request signal transmitting step is put into a request signaltransmitted in the second request signal transmitting step and therequest signal is transmitted via at least one relay station or directlyto the receiving station; the communication path determining stepcomprises a communication speed determining step wherein the receivingstation determines a communication speed on each communication pathbetween the transmitting station and the receiving station, based on theinterstation communication speed between each pair of stationsconstituting a communication path between the transmitting station andthe receiving station; and a communication path selecting step wherein acommunication path is selected based on communication speeds onrespective communication paths determined in the communication speeddetermining step.

In the mobile communication system (communication path determiningmethod) according to the present invention, the relay station measuresthe interference level at the relay station itself when receiving arequest signal having been transmitted from the transmitting station oranother relay station, and determines the interstation communicationspeed between the relay station and the transmitting station or theother relay station as a source of the request signal on the basis ofthe measured interference level. Then each relay station puts theinterstation communication speed information about the determinedinterstation communication speed into a request signal and transmits therequest signal to the receiving station. The receiving station measuresthe interference level at the receiving station itself when receivingthe request signal having been transmitted from the transmitting stationor the relay station, and determines the interstation communicationspeed between the receiving station and the transmitting station or therelay station as a source of the request signal on the basis of themeasured interference level. This permits the receiving station todetermine the total communication speed between the transmitting stationand the receiving station on the basis of the interstation communicationspeed between each pair of stations constituting a communication pathbetween the transmitting station and the receiving station and todetermine the communication path with the highest communication speed orthe communication path satisfying the required line quality on the basisof the communication speed. Then the receiving station transmits theinformation about the determined communication path to the transmittingstation, whereby the transmitting station can transmit packets to thereceiving station in accordance with the determined communication path.

The above mobile communication system may be configured as follows: thereceiving station comprises request signal receiving means for receivinga request signal transmitted from the transmitting station or the relaystation; interference level measuring means for measuring aninterference level at the receiving station when the request signalreceiving means receives a request signal; and request response signaltransmitting means for transmitting a request response signal containingthe interference level measured by the interference level measuringmeans, to the transmitting station or the relay station as a source ofthe request signal; the relay station comprises request signal receivingmeans for receiving a request signal transmitted from the transmittingstation or another relay station; interference level measuring means formeasuring an interference level at the host relay station when therequest signal receiving means receives a request signal; request signaltransmitting means for transmitting a request signal; request responsesignal receiving means for receiving a request response signaltransmitted from the receiving station or a second other relay station,in response to the request signal transmitted by the request signaltransmitting means; and request response signal transmitting means fortransmitting a request response signal containing the interference levelmeasured by the interference level measuring means, and the interferencelevel included in the request response signal received by the requestresponse signal receiving means, to the transmitting station or theother relay station as a source of the request signal; the transmittingstation comprises the communication path determining means having:request signal transmitting means for transmitting a request signal;request response signal receiving means for receiving a request responsesignal to the request signal transmitted by the request signaltransmitting means; interstation communication speed determining meansfor determining an interstation communication speed between each pair ofstations constituting a communication path, based on the interferencelevel included in the request response signal; communication speeddetermining means for determining a communication speed on acommunication path from the transmitting station to the receivingstation on the basis of the interstation communication speed determinedby the interstation communication speed determining means; andcommunication path selecting means for selecting a communication path onthe basis of communication speeds on respective communication pathsdetermined by the communication speed determining means.

The above communication path determining method may be configured tofurther comprise a request signal transmitting step wherein thetransmitting station transmits a request signal to the receiving stationor the relay station; a second request signal transmitting step whereinwhen the relay station receives a request signal, the relay stationtransmits a request signal to the receiving station or another relaystation; an interference level measuring step wherein the receivingstation or the relay station receiving the request signal transmitted inthe request signal transmitting step or in the second request signaltransmitting step measures an interference level at the receivingstation or the relay station; and a request response signal transmittingstep wherein the receiving station or the relay station transmits arequest response signal containing the interference level measured inthe interference level measuring step to the transmitting station or therelay station as a source of the request signal; and configured asfollows: the communication path determining step comprises aninterstation communication speed determining step wherein thetransmitting station determines an interstation communication speedbetween each pair of stations constituting a communication path, basedon the interference level included in the request response signaltransmitted via at least one relay station or directly to thetransmitting station in the request response signal transmitting step; acommunication speed determining step wherein the transmitting stationdetermines a communication speed on each communication path between thetransmitting station and the receiving station, based on theinterstation communication speed between each pair of stationsdetermined in the interstation communication speed determining step; anda communication path selecting step wherein the transmitting stationselects a communication path on the basis of communication speeds onrespective communication paths determined in the communication speeddetermining step.

When the request response signal containing the interference level ateach station constituting a communication path is transmitted to thetransmitting station in this way, the transmitting station is able todetermine the interstation communication speed between each pair ofstations constituting a communication path on the basis of theinterference level at each station and to determine the communicationspeed between the transmitting station and the receiving station on thebasis of the determined interstation communication speeds. Thetransmitting station is able to determine the communication path, basedon the communication speeds on the respective communication pathsdetermined in this way.

The above mobile communication system may be configured as follows: therelay station comprises request signal receiving means for receiving arequest signal transmitted from the transmitting station or anotherrelay station; interference level measuring means for measuring aninterference level at the host relay station when the request signalreceiving means receives a request signal; and request signaltransmitting means for transmitting a request signal containing theinterference level measured by the interference level measuring meansand, where the request signal is one transmitted from another relaystation, also containing an interference level included in the requestsignal; the receiving station comprises the communication pathdetermining means having: request signal receiving means for receiving arequest signal transmitted from the transmitting station or the relaystation; interference level measuring means for measuring aninterference level at the receiving station when the request signalreceiving means receives a request signal; interstation communicationspeed determining means for determining an interstation communicationspeed between each pair of stations constituting a communication path,based on the interference level measured by the interference levelmeasuring means and, where the request signal is one transmitted fromthe relay station, also based on the interference level included in therequest signal; communication speed determining means for determining acommunication speed on each communication path between the transmittingstation and the receiving station on the basis of the interstationcommunication speed determined by the interstation communication speeddetermining means; and communication path selecting means for selectinga communication path, based on communication speeds on respectivecommunication paths determined by the communication speed determiningmeans.

The above communication path determining method may be configured tofurther comprise a request signal transmitting step wherein thetransmitting station transmits a request signal to the receiving stationor the relay station; a second request signal transmitting step whereinwhen the relay station receives a request signal, the relay stationtransmits a request signal to the receiving station or another relaystation; and an interference level measuring step wherein the receivingstation or the relay station receiving the request signal transmitted inthe request signal transmitting step or in the second request signaltransmitting step measures an interference level at the receivingstation or the relay station; and configured as follows: theinterference level measured in the interference level measuring step isput into a request signal and the request signal is transmitted via atleast one relay station or directly to the receiving station; thecommunication path determining step comprises an interstationcommunication speed determining step wherein the receiving stationdetermines an interstation communication speed between each pair ofstations constituting a communication path, based on an interferencelevel included in a request signal; a communication speed determiningstep wherein the receiving station determines a communication speed oneach communication path between the transmitting station and thereceiving station on the basis of the interstation communication speeddetermined in the interstation communication speed determining step; anda communication path selecting step wherein the receiving stationselects a communication path, based on communication speeds onrespective communication paths determined in the communication speeddetermining step.

When the interference level at each station forming a communication pathis put into a request signal to be transmitted to the receiving station,the receiving station is able to determine the interstationcommunication speed between each pair of stations forming thecommunication path on the basis of the interference level at eachstation and to determine the communication speed between thetransmitting station and the receiving station on the basis of thedetermined interstation communication speed. The receiving station isable to determine the communication path, based on the communicationspeeds on the respective communication paths determined in this way.

The above mobile communication system (the communication pathdetermining method) may be configured so that the communication pathfrom the transmitting station to the receiving station determined by thecommunication path determining means (or in the communication pathdetermining step) is also applied to cases of transmitting packets fromthe receiving station to the transmitting station.

In cases of carrying out bidirectional communication between thetransmitting station and the receiving station, communication is alsocarried out through the communication path determined by the abovemobile communication system (the communication path determining method)on the occasion of transmitting packets from the receiving station tothe transmitting station, which is preferable in that it is feasible toomit the step of again determining the communication path from thereceiving station to the transmitting station. On this occasion, thecommunication speed may be varied according to transmission powers ofthe transmitting station and the receiving station.

The above mobile communication system (communication path determiningmethod) may be configured so that, where there exist a plurality ofcommunication paths satisfying the required line quality, thecommunication path determining means (the communication path determiningstep) determines a path with a smallest hop count between thetransmitting station and the receiving station, as a communication path.

Increase of the hop count can bring about a delay at each relay stationand, where there are a plurality of communication paths satisfying therequired line quality, it is preferable to select the communication pathwith the smallest hop count. When a predetermined delay time is given asthe required line quality, a hop count permitted for clearing the givendelay time can be defined as a threshold. The required line quality canbe satisfied by determining a communication path with a hop countsmaller than the threshold.

The above mobile communication system (communication path determiningmethod) may be configured so that, where there exist a plurality ofcommunication paths satisfying the required line quality, thecommunication path determining means (the communication path determiningstep) determines a path with a small total of transmission powers at thetransmitting station and at the relay station forming the communicationpath, as a communication path.

Decrease in the total of transmission powers can suppress increase ininterference noise due to relaying of packet transmission at the relaystation, and, where there are a plurality of communication pathssatisfying the required line quality, it is preferable to select thecommunication path with the small total of transmission powers.

The above mobile communication system (communication path determiningmethod) may be configured so that, where there exist a plurality ofcommunication paths satisfying the required line quality, thecommunication path determining means (the communication path determiningstep) determines a path with a small transmission power at thetransmitting station, as a communication path.

In the case where power is supplied to the relay station and thereceiving station, it is preferable to minimize the transmission powerat the transmitting station which is normally comprised of a cell phoneor the like.

The above mobile communication system (communication path determiningmethod) may be configured so that the communication path determiningmeans (the communication path determining step) determines acommunication path out of communication paths having a hop count betweenthe transmitting station and the receiving station of not more than apredetermined threshold.

Increase of the hop count can bring about a delay at each relay stationand it is preferable to preliminarily define a hop count of an upperlimit in determining a communication path. When a predetermined delaytime is given as the required line quality, a hop count permitted forclearing the given delay time can be defined as a threshold. Therequired line quality can be satisfied by determining a communicationpath with a hop count smaller than the threshold.

In the above mobile communication system (communication path determiningmethod), it is preferable to vary the communication speed by changing amodulation system or a spreading system.

A transmitting station according to the present invention is atransmitting station applied to a mobile communication system andconfigured to transmit a packet to a receiving station through acommunication path with an intermediary of at least one relay station orthrough a communication path without an intermediary of a relay station,the transmitting station comprising communication path determining meansfor determining a communication path with a largest communication speedor a communication path satisfying a required line quality, based oninterference levels of respective signals received at a relay stationconstituting a communication path to the receiving station and at thereceiving station.

A program for the transmitting station according to the presentinvention is a program applied to a mobile communication system and, fortransmitting a packet from the transmitting station to a receivingstation through a communication path with an intermediary of at leastone relay station or through a communication path without anintermediary of a relay station, letting a computer execute acommunication path determining step of determining a communication pathwith a largest communication speed or a communication path satisfying arequired line quality, based on interference levels of respectivesignals received at a relay station constituting a communication pathbetween the transmitting station and the receiving station and at thereceiving station.

For determining a communication path by multihop connection or by singlehop connection, the transmitting station according to the presentinvention determines the communication path with the largestcommunication speed or the communication path satisfying thepredetermined line quality, based on the interference levels of therespective signals received at the relay station forming thecommunication path and at the receiving station, whereby it can achieveimplementation of fast communication.

The transmitting station program according to the present invention cansubstantialize the aforementioned transmitting station when executed bythe computer, and determines the communication path with the largestcommunication speed or the communication path satisfying the requiredline quality, based on the interference levels of the respective signalsat the relay station forming the communication path and at the receivingstation, whereby it can achieve implementation of fast communication.

The above transmitting station may be configured to comprise thecommunication path determining means having request signal transmittingmeans for transmitting a request signal to request communication at apredetermined communication speed; and request response signal receivingmeans for receiving a request response signal containing communicationpropriety information about propriety of communication, transmitted inresponse to the request signal transmitted by the request signaltransmitting means; and configured so that when that it is impossible toperform the communication at the predetermined communication speed isdetermined based on the communication propriety information included inthe request response signal received by the request response signalreceiving means, the transmitting station transmits the request signalwhile stepwise decreasing the request communication speed, before adetermination of being communicable is made and so that when it isdetermined that it is possible to perform the communication at thepredetermined communication speed, the transmitting station starts thecommunication with the receiving station or the relay station at thecommunication speed determined as communicable.

The above transmitting station program may be configured so that thecommunication path determining step comprises a request signaltransmitting step of transmitting a request signal to requestcommunication at a predetermined communication speed; and a requestresponse signal receiving step of receiving a request response signalcontaining communication propriety information about propriety ofcommunication, transmitted in response to the request signal transmittedin the request signal transmitting step; and configured so that whenthat it is impossible to perform the communication at the predeterminedcommunication speed is determined based on the communication proprietyinformation included in the request response signal received in therequest response signal receiving step, the request signal istransmitted while stepwise decreasing the request communication speed,before a determination of being communicable is made and so that when itis determined that it is possible to perform the communication at thepredetermined communication speed, the communication is started with thereceiving station or with the relay station at the communication speeddetermined as communicable.

In the transmitting station according to the present invention (orthrough execution of the transmitting station program), the requestsignal transmitting means (the request signal transmitting step)transmits the request signal to request the communication at thepredetermined communication speed and it is determined whether it ispossible to perform the communication at the predetermined communicationspeed, based on the communication propriety information included in therequest response signal transmitted in response to the request signal.When the result of the determination is that it is possible to performthe communication at the predetermined communication speed, thecommunication is started at the communication speed; when it isimpossible to perform the communication at the predeterminedcommunication speed, the request signal is transmitted while stepwisedecreasing the request communication speed, before a determination ofbeing communicable is made. This enables the communication at themaximum communication speed available for communication between thetransmitting station and the receiving station.

The above transmitting station may be configured to comprise thecommunication path determining means: having request signal transmittingmeans for transmitting a request signal to request communication at apredetermined communication speed; and request response signal receivingmeans for receiving a request response signal containing communicationpropriety information about propriety of communication, transmitted inresponse to the request signal transmitted by the request signaltransmitting means; and configured so that when that it is possible toperform the communication at the predetermined communication speed isdetermined based on the communication propriety information included inthe request response signal received by the request response signalreceiving means, the request signal is transmitted while stepwiseincreasing the request communication speed, before a determination ofbeing uncommunicable is made; and so that when it is determined that itis impossible to perform the communication at the predeterminedcommunication speed, the communication is started with the receivingstation or with the relay station at a maximum communication speed outof communication speeds determined as communicable.

The above transmitting station program may be configured so that thecommunication path determining step comprises a request signaltransmitting step of transmitting a request signal to requestcommunication at a predetermined communication speed; and a requestresponse signal receiving step of receiving a request response signalcontaining communication propriety information on propriety ofcommunication, transmitted in response to the request signal transmittedin the request signal transmitting step; and configured so that whenthat it is possible to perform the communication at the predeterminedcommunication speed is determined based on the communication proprietyinformation included in the request response signal received in therequest response signal receiving step, the request signal istransmitted while stepwise increasing the request communication speed,before a determination of being uncommunicable is made; and so that whenit is determined that it is impossible to perform the communication atthe predetermined communication speed, the communication is started withthe receiving station or with the relay station at a maximumcommunication speed out of communication speeds determined ascommunicable.

In the transmitting station according to the present invention (orthrough execution of the transmitting station program), the requestsignal transmitting means (the request signal transmitting step)transmits the request signal at the predetermined communication speed,and whether it is possible to perform the communication at thepredetermined communication speed is determined based on the informationon propriety of communication included in the request response signaltransmitted in response to the request signal. When the result of thedetermination is that it is possible to perform the communication at thepredetermined communication speed, the request signal is transmittedwile stepwise increasing the request communication speed, before adetermination of being uncommunicable is made; with a determination ofbeing uncommunicable, the communication is started at a maximumcommunication speed out of communication speeds determined ascommunicable. This enables the communication at the maximumcommunication speed available for communication between the transmittingstation and the receiving station. It is also feasible to establish thecommunication at the first communicable communication speed, which candecrease the period of time before the establishment of connection.

The above transmitting station may be configured to comprise thecommunication path determining means having: request signal transmittingmeans for transmitting a request signal; request response signalreceiving means for receiving a request response signal to the requestsignal transmitted by the request signal transmitting means;interstation communication speed determining means for determining aninterstation communication speed between the transmitting station andthe receiving station or the relay station as a source of the requestresponse signal, based on an interference level at the receiving stationor the relay station as a source of the request response signal,included in the request response signal; communication speed determiningmeans for determining a communication speed on a communication path fromthe transmitting station to the receiving station, based on theinterstation communication speed determined by the interstationcommunication speed determining means and, where the request responsesignal is one transmitted from the relay station, also based oninterstation communication speed information between each pair ofstations constituting a communication path from the relay station to thereceiving station, included in the request response signal; andcommunication path selecting means for selecting a communication path onthe basis of communication speeds on respective communication pathsdetermined by the communication speed determining means.

The above transmitting station program may be configured so that thecommunication path determining step comprises a request signaltransmitting step of transmitting a request signal; a request responsesignal receiving step of receiving a request response signal to therequest signal transmitted in the request signal transmitting step; aninterstation communication speed determining step of determining aninterstation communication speed between the transmitting station andthe receiving station or the relay station as a source of the requestresponse signal, based on an interference level at the receiving stationor the relay station as a source of the request response signal,included in the request response signal; a communication speeddetermining step of determining a communication speed on a communicationpath from the transmitting station to the receiving station, based onthe interstation communication speed determined in the interstationcommunication speed determining step and, where the request responsesignal is one transmitted from the relay station, also based oninterstation communication speed information between each pair ofstations constituting a communication path from the relay station to thereceiving station, included in the request response signal; and acommunication path selecting step of selecting a communication path onthe basis of communication speeds on respective communication pathsdetermined in the communication speed determining step.

In the transmitting station according to the present invention (orthrough execution of the transmitting station program), the interstationcommunication speed determining means (the interstation communicationspeed communicating step) determines the interstation communicationspeed between the transmitting station and the receiving station or therelay station as a source of the request response signal, based on theinterference level included in the request response signal transmittedfrom the receiving station or the relay station. The request responsesignal receiving means (the request response signal receiving step)receives the interstation communication speed information about theinterstation communication speed between each pair of stationsconstituting the communication path between the transmitting station andthe receiving station. This permits the transmitting station todetermine the total communication speed between the transmitting stationand the receiving station on the basis of the interstation communicationspeed between each pair of stations constituting the communication pathbetween the transmitting station and the receiving station and todetermine the communication path with the largest communication speed orthe communication path satisfying the required line quality on the basisof the communication speed.

The above transmitting station may be configured to comprise thecommunication path determining means having: request signal transmittingmeans for transmitting a request signal; request response signalreceiving means for receiving a request response signal to the requestsignal transmitted by the request signal transmitting means;communication speed determining means for determining a communicationspeed from the transmitting station to the receiving station, based oninterstation communication speed information between each pair ofstations constituting a communication path from the transmitting stationto the receiving station, included in the request response signalreceived by the request response signal receiving means; andcommunication path selecting means for selecting a communication path onthe basis of communication speeds on respective communication pathsdetermined by the communication speed determining means.

The above transmitting station program may be configured so that thecommunication path determining step comprises a request signaltransmitting step of transmitting a request signal; a request responsesignal receiving step of receiving a request response signal to therequest signal transmitted in the request signal transmitting step; acommunication speed determining step of determining a communicationspeed from the transmitting station to the receiving station, based oninterstation communication speed information between each pair ofstations constituting a communication path from the transmitting stationto the receiving station, included in the request response signalreceived in the request response signal receiving step; and acommunication path selecting step of selecting a communication path onthe basis of communication speeds on respective communication pathsdetermined in the communication speed determining step.

In the transmitting station according to the present invention (orthrough execution of the transmitting station program), the requestresponse receiving means (the request response signal receiving step)receives the request response signal containing the interstationcommunication speed information about the interstation communicationspeed between each pair of stations constituting the communication pathbetween the transmitting station and the receiving station. This permitsthe transmitting station to determine the total communication speedbetween the transmitting station and the receiving station on the basisof the interstation communication speed between each pair of stationsconstituting the communication path between the transmitting station andthe receiving station and to determine the communication path with thelargest communication speed or the communication path satisfying therequired line quality on the basis of the communication speed.

The above transmitting station may be configured to comprise thecommunication path determining means: having request signal transmittingmeans for transmitting a request signal; request response signalreceiving means for receiving a request response signal to the requestsignal transmitted by the request signal transmitting means;interstation communication speed determining means for determining aninterstation communication speed between each pair of stationsconstituting a communication path, based on an interference level ateach station included in the request response signal; communicationspeed determining means for determining a communication speed on thecommunication path from the transmitting station to the receivingstation on the basis of the interstation communication speed determinedby the interstation communication speed determining means; andcommunication path selecting means for selecting a communication path onthe basis of communication speeds on respective communication pathsdetermined by the communication speed determining means.

The above transmitting station program may be configured so that thecommunication path determining step comprises a request signaltransmitting step of transmitting a request signal; a request responsesignal receiving step of receiving a request response signal to therequest signal transmitted in the request signal transmitting step; aninterstation communication speed determining step of determining aninterstation communication speed between each pair of stationsconstituting a communication path, based on an interference levelincluded in the request response signal; a communication speeddetermining step of determining a communication speed on thecommunication path from the transmitting station to the receivingstation on the basis of the interstation communication speed determinedin the interstation communication speed determining step; and acommunication path selecting step of selecting a communication path onthe basis of communication speeds on respective communication pathsdetermined in the communication speed determining step.

In the transmitting station according to the present invention (orthrough execution of the transmitting station program), the interstationcommunication speed determining means (the interstation communicationspeed determining step) is able to determine the interstationcommunication speed between each pair of stations constituting thecommunication path, based on the interference level at each stationincluded in the request response signal, and the communication speeddetermining means (the communication speed determining step) is able todetermine the communication speed between the transmitting station andthe receiving station, based on the interstation communication speedbetween each pair of stations thus determined. The transmitting stationis able to determine the communication path, based on the communicationspeeds on the respective communication paths determined in this way.

The above transmitting station (transmitting station program) may beconfigured so that, where there exist a plurality of communication pathssatisfying the required line quality, the communication path determiningmeans (communication path determining step) determines a path with asmallest hop count between the transmitting station and the receivingstation, as a communication path.

Increase of the hop count can bring about a delay at each relay stationand, where there are a plurality of communication paths satisfying therequired line quality, it is preferable to select the communication pathwith the smallest hop count. When a predetermined delay time is given asthe required line quality, a hop count permitted for clearing the givendelay time can be defined as a threshold. The required line quality canbe satisfied by determining a communication path with a hop countsmaller than the threshold.

The above transmitting station (transmitting station program) may beconfigured so that, where there exist a plurality of communication pathssatisfying the required line quality, the communication path determiningmeans (the communication path determining step) determines a path with asmall total of transmission powers at the transmitting station and atthe relay station forming the communication path, as a communicationpath.

Decrease in the total of transmission powers can suppress increase ininterference noise due to relaying of packet transmission at the relaystation, and, where there are a plurality of communication pathssatisfying the required line quality, it is preferable to select thecommunication path with the small total of transmission powers.

The above transmitting station (transmitting station program) may beconfigured so that, where there exist a plurality of communication pathssatisfying the required line quality, the communication path determiningmeans (the communication path determining step) determines a path with asmall transmission power at the transmitting station, as a communicationpath.

In the case where power is supplied to the relay station and to thereceiving station, it is preferable to minimize the transmission powerat the transmitting station which is normally comprised of a cell phoneor the like.

The above transmitting station (transmitting station program) may beconfigured so that the communication path determining means (thecommunication path determining step) determines a communication path outof communication paths having a hop count between the transmittingstation and the receiving station of not more than a predeterminedthreshold.

Increase of the hop count can bring about a delay at each relay stationand it is thus preferable to preliminarily define a hop count of anupper limit in determining a communication path. When a predetermineddelay time is given as the required line quality, a hop count permittedfor clearing the given delay time can be defined as a threshold. Therequired line quality can be satisfied by determining a communicationpath with a hop count smaller than the threshold.

In the above transmitting station (transmitting station program), it ispreferable to vary the communication speed, by changing a modulationsystem or a spreading system.

A receiving station according to the present invention is a receivingstation applied to a mobile communication system and configured toreceive a packet from a transmitting station through a communicationpath with an intermediary of at least one relay station or through acommunication path without an intermediary of a relay station, thereceiving station comprising communication path determining means fordetermining a communication path with a largest communication speed or acommunication path satisfying a required line quality, based oninterference levels of respective signals received at a relay stationconstituting a communication path between the transmitting station andthe receiving station, and at the receiving station.

A program for the receiving station according to the present inventionis a program applied to a mobile communication system and, for receivinga packet from a transmitting station through a communication path withan intermediary of at least one relay station or through a communicationpath without an intermediary of a relay station, letting a computerexecute a communication path determining step of determining acommunication path with a largest communication speed or a communicationpath satisfying a required line quality, based on interference levels ofrespective signals received at a relay station constituting acommunication path between the transmitting station and the receivingstation, and at the receiving station.

For determining a communication path by multihop connection or by singlehop connection, the receiving station according to the present inventiondetermines the communication path with the largest communication speedor the communication path satisfying the required line quality, based onthe interference levels of the respective signals received at the relaystation forming the communication path and at the receiving station,whereby it can achieve implementation of fast communication.

The receiving station program according to the present invention cansubstantialize the aforementioned transmitting station when executed bythe computer, and determines the communication path with the largestcommunication speed or the communication path satisfying the requiredline quality, based on the interference levels of the respective signalsreceived at the relay station forming the communication path and at thereceiving station, whereby it can achieve implementation of fastcommunication.

The above receiving station may be configured to comprise thecommunication path determining means having: request signal receivingmeans for receiving a request signal transmitted from the transmittingstation or the relay station; interference level measuring means formeasuring an interference level at the receiving station when therequest signal receiving means receives a request signal; interstationcommunication speed determining means for determining an interstationcommunication speed between the receiving station and the transmittingstation or the relay station as a source of the request signal, based onthe interference level measured by the interference level measuringmeans; communication speed determining means for determining acommunication speed between the transmitting station and the receivingstation, based on the interstation communication speed determined by theinterstation communication speed determining means and, where therequest signal is one received from the relay station, also based oninterstation communication speed information between each pair ofstations constituting a communication path from the transmitting stationto the relay station, included in the request signal; and communicationpath selecting means for selecting a communication path, based oncommunication speeds on respective communication paths determined by thecommunication speed determining means.

The above receiving station program may be configured so that thecommunication path determining step comprises a request signal receivingstep of receiving a request signal transmitted from the transmittingstation or the relay station; an interference level measuring step ofmeasuring an interference level at the receiving station when a requestsignal is received in the request signal receiving step; an interstationcommunication speed determining step of determining an interstationcommunication speed between the receiving station and the transmittingstation or the relay station as a source of the request signal, based onthe interference level measured in the interference level measuringstep; a communication speed determining step of determining acommunication speed between the transmitting station and the receivingstation, based on the interstation communication speed determined in theinterstation communication speed determining step and, where the requestsignal is one received from the relay station, also based oninterstation communication speed information between each pair ofstations constituting a communication path from the transmitting stationto the relay station, included in the request signal; and acommunication path selecting step of selecting a communication path,based on communication speeds on respective communication pathsdetermined in the communication speed determining step.

In the case of the receiving station according to the present invention(or through execution of the receiving station program), the receivingstation measures the interference level at the receiving station itselfwhen receiving a request signal having been transmitted from thetransmitting station or the relay station, and determines theinterstation communication speed between the receiving station and thetransmitting station or the relay station as a source of the requestsignal on the basis of the measured interference level. In the receivingstation, the request signal receiving means (the request signalreceiving step) receives the request signal containing the interstationcommunication speed information about the interstation communicationspeed between each pair of stations forming the communication pathbetween the transmitting station and the receiving station. This permitsthe receiving station to determine the total communication speed betweenthe transmitting station and the receiving station on the basis of theinterstation communication speed between each pair of stationsconstituting the communication path between the transmitting station andthe receiving station and to determine the communication path with thelargest communication speed or the communication path satisfying therequired line quality on the basis of the communication speed. Thereceiving station then transmits the information about the determinedcommunication path to the transmitting station, whereby the transmittingstation can transmit a packet to the receiving station in accordancewith the determined communication path.

The above receiving station may be configured to comprise thecommunication path determining means having: request signal receivingmeans for receiving a request signal transmitted from the transmittingstation or the relay station; interference level measuring means formeasuring an interference level at the receiving station when therequest signal receiving means receives a request signal; interstationcommunication speed determining means for determining an interstationcommunication speed between each pair of stations constituting acommunication path, based on the interference level measured by theinterference level measuring means and, where the request signal is onetransmitted from the relay station, also based on an interference levelincluded in the request signal; communication speed determining meansfor determining a communication speed between the transmitting stationand the receiving station on the basis of the interstation communicationspeed determined by the interstation communication speed determiningmeans; and communication path selecting means for selecting acommunication path, based on communication speeds on respectivecommunication paths determined by the communication speed determiningmeans.

The above receiving station program may be configured so that thecommunication path determining step comprises a request signal receivingstep of receiving a request signal transmitted from the transmittingstation or the relay station; an interference level measuring step ofmeasuring an interference level at the receiving station when a requestsignal is received in the request signal receiving step; an interstationcommunication speed determining step of determining an interstationcommunication speed between each pair of stations constituting acommunication path, based on the interference level measured in theinterference level measuring step and based on an interference levelincluded in the request signal; a communication speed determining stepof determining a communication speed between the transmitting stationand the receiving station on the basis of the interstation communicationspeed determined in the interstation communication speed determiningstep; and a communication path selecting step of selecting acommunication path, based on communication speeds on respectivecommunication paths determined in the communication speed determiningstep.

In the receiving station according to the present invention (or throughexecution of the receiving station program), the interstationcommunication speed determining means (the interstation communicationspeed determining step) is able to determine the interstationcommunication speed between each pair of stations constituting acommunication path, based on the interference level at each stationincluded in the request signal, and the communication speed determiningmeans (the communication speed determining step) is able to determinethe communication speed between the transmitting station and thereceiving station, based on the interstation communication speed betweeneach pair of stations thus determined. The receiving station is able todetermine the communication path, based on the communication speeds onthe respective communication paths determined in this way.

The above receiving station (receiving station program) may beconfigured so that, where there exist a plurality of communication pathssatisfying the required line quality, the communication path determiningmeans (the communication path determining step) determines a path with asmallest hop count between the transmitting station and the receivingstation, as a communication path.

Increase of the hop count can bring about a delay at each relay stationand, where there are a plurality of communication paths satisfying therequired line quality, it is preferable to select the communication pathwith the smallest hop count. When a predetermined delay time is given asthe required line quality, a hop count permitted for clearing the givendelay time can be defined as a threshold. The required line quality canbe satisfied by determining a communication path with a hop countsmaller than the threshold.

The above receiving station (receiving station program) may beconfigured so that, where there exist a plurality of communication pathssatisfying the required line quality, the communication path determiningmeans (the communication path determining step) determines a path with asmall total of transmission powers at the transmitting station and atthe relay station constituting the communication path, as acommunication path.

Decrease in the total of transmission powers can suppress increase ininterference noise due to relaying of packet transmission at the relaystation, and, where there are a plurality of communication pathssatisfying the required line quality, it is preferable to select thecommunication path with the small total of transmission powers.

The above receiving station (receiving station program) may beconfigured so that, where there exist a plurality of communication pathssatisfying the required line quality, the communication path determiningmeans (the communication path determining step) determines a path with asmall transmission power at the transmitting station, as a communicationpath.

In the case where power is supplied to the relay station and to thereceiving station, it is preferable to minimize the transmission powerat the transmitting station which is normally comprised of a cell phoneor the like.

The above receiving station (receiving station program) may beconfigured so that the communication path determining means (thecommunication path determining step) determines a communication path outof communication paths having a hop count of not more than apredetermined threshold.

Increase of the hop count can bring about a delay at each relay stationand it is thus preferable to preliminarily define a hop count of anupper limit in determining a communication path. When a predetermineddelay time is given as the required line quality, a hop count permittedfor clearing the given delay time can be defined as a threshold. Therequired line quality can be satisfied by determining a communicationpath with a hop count smaller than the threshold.

In the above receiving station (receiving station program, it ispreferable to vary the communication speed, by changing a modulationsystem or a spreading system.

A receiving station according to the present invention is a receivingstation comprising: request signal receiving means for receiving arequest signal transmitted from a transmitting station through acommunication path with an intermediary of at least one relay station orthrough a communication path without an intermediary of a relay station;interference level measuring means for measuring an interference levelat the receiving station when the request signal receiving meansreceives a request signal; communication propriety determining means fordetermining whether it is possible to perform communication at acommunication speed included in the request signal, based on theinterference level measured by the interference level measuring means;and request response signal transmitting means for transmitting arequest response signal containing information on propriety ofcommunication determined by the communication propriety determiningmeans, through the communication path to the transmitting station.

A program for the receiving station according to the present inventionis a program applied to a mobile communication system and, for receivinga packet from a transmitting station through a communication path withan intermediary of at least one relay station or through a communicationpath without an intermediary of a relay station, letting a computerexecute: a request signal receiving step of receiving a request signaltransmitted from the transmitting station through a communication pathwith an intermediary of at least one relay station or through acommunication path without an intermediary of a relay station; aninterference level measuring step of measuring an interference level atthe receiving station when a request signal is received in the requestsignal receiving step; a communication propriety determining step ofdetermining whether it is possible to perform communication at acommunication speed included in the request signal, based on theinterference level measured in the interference level measuring step;and a request response signal transmitting step of transmitting arequest response signal containing information on propriety ofcommunication determined in the communication propriety determiningstep, through the communication path to the transmitting station.

The receiving station according to the present invention (the receivingstation program as executed) measures the interference level at thereceiving station when receiving a request signal, and determineswhether it is possible to perform the communication requested by therequest signal, on the basis of the measured interference level. Thenthe receiving station puts the information about propriety ofcommunication based on the result of this determination into a requestresponse signal and transmits the request response signal to thetransmitting station, whereby the transmitting station can acquire theinformation about propriety of communication at the receiving stationand use it on the occasion of determining the communication path.

Another receiving station according to the present invention is areceiving station comprising: request signal receiving means forreceiving a request signal transmitted from the transmitting station orfrom the relay station; interference level measuring means for measuringan interference level at the receiving station when the request signalreceiving means receives a request signal; interstation communicationspeed determining means for determining an interstation communicationspeed between the receiving station and the transmitting station or therelay station as a source of the request signal, based on theinterference level measured by the interference level measuring means;and request response signal transmitting means for transmitting arequest response signal containing the interstation communication speedinformation determined by the interstation communication speeddetermining means, to the transmitting station or the relay station as asource of the request signal.

A program for the receiving station according to the present inventionis a program applied to a mobile communication system and, for receivinga packet from a transmitting station through a communication path withan intermediary of at least one relay station or through a communicationpath without an intermediary of a relay station, letting a computerexecute: a request signal receiving step of receiving a request signaltransmitted from the transmitting station or from a relay station; aninterference level measuring step of measuring an interference level atthe receiving station when a request signal is received in the requestsignal receiving step; an interstation communication speed determiningstep of determining an interstation communication speed between thereceiving station and the transmitting station or the relay station as asource of the request signal, based on the interference level measuredin the interference level measuring step; and a request response signaltransmitting step of transmitting a request response signal containingthe interstation communication speed information determined in theinterstation communication speed determining step, to the transmittingstation or the relay station as a source of the request signal.

The receiving station according to the present invention (the receivingstation program as executed) measures the interference level at thereceiving station when receiving a request signal, and determines theinterstation communication speed between the receiving station and thetransmitting station or the relay station as a source of the requestsignal on the basis of the measured interference level. Then thereceiving station puts the information about the interstationcommunication speed into a request response signal and transmits it tothe transmitting station, whereby the transmitting station can acquirethe interstation communication speed information at the receivingstation and use it on the occasion of determining the communicationpath.

A relay station according to the present invention is a relay stationcomprising: request signal receiving means for receiving a requestsignal transmitted from a transmitting station through a communicationpath with an intermediary of at least one relay station or through acommunication path without an intermediary of a relay station;interference level measuring means for measuring an interference levelat the host relay station when the request signal receiving meansreceives a request signal; communication propriety determining means fordetermining whether it is possible to perform communication at acommunication speed included in the request signal, based on theinterference level measured by the interference level measuring means;and request response signal transmitting means for transmitting arequest response signal containing information on propriety ofcommunication determined by the communication propriety determiningmeans, through the communication path to the transmitting station.

A program for the relay station according to the present invention is aprogram applied to a multihop mobile communication system and, forrelaying transmission of a packet from a transmitting station to areceiving station, letting a computer execute: a request signalreceiving step of receiving a request signal transmitted from thetransmitting station through a communication path with an intermediaryof at least one relay station or through a communication path without anintermediary of a relay station; an interference level measuring step ofmeasuring an interference level at the host relay station when a requestsignal is received in the request signal receiving step; a communicationpropriety determining step of determining whether it is possible toperform communication at a communication speed included in the requestsignal, based on the interference level measured in the interferencelevel measuring step; and a request response signal transmitting step oftransmitting a request response signal containing information onpropriety of communication determined in the communication proprietydetermining step, through the communication path to the transmittingstation.

The relay station according to the present invention (the relay stationprogram as executed) measures the interference level at the relaystation itself when receiving a request signal, and determines whetherit is possible to perform the communication requested by the requestsignal, on the basis of the interference level. Then the relay stationputs the information about propriety of communication based on theresult of this determination into a request response signal andtransmits it to the transmitting station, whereby the transmittingstation can acquire the communication propriety information at the relaystation and use the communication propriety information on the occasionof determining the communication path.

The above relay station may be configured to further comprise requestsignal transmitting means for transmitting a request signal to thereceiving station or another relay station only when the communicationpropriety determining means determines that it is possible to performthe communication; and request response signal receiving means forreceiving a request response signal to the request signal transmitted bythe request signal transmitting means.

The above relay station program may be configured to let the computerfurther execute: a request signal transmitting step of transmitting arequest signal to the receiving station or another relay station onlywhen the communication propriety determining step results in determiningthat it is possible to perform the communication; and a request responsesignal receiving step of receiving a request response signal to therequest signal transmitted in the request signal transmitting step.

When a path between certain stations forming a communication path isuncommunicable, it is impossible to perform the communication using thecommunication path; therefore, only when the communication proprietydetermining means (the communication propriety determining step)determines that it is possible to perform the communication through therelay station, a further request signal is transmitted to search for acommunication path toward the receiving station; when it is determinedthat it is impossible to perform the communication, the transmission ofthe request signal is terminated at that point and the request responsesignal containing the information indicating the uncommunicable state istransmitted, whereby it is feasible to prevent transmission ofineffectual request signals and thus achieve increase of efficiency ofthe mobile communication system including the relay station.

Another relay station according to the present invention may be a relaystation comprising: request signal receiving means for receiving arequest signal transmitted from a transmitting station or from anotherrelay station; interference level measuring means for measuring aninterference level at the host relay station when the request signalreceiving means receives a request signal; request signal transmittingmeans for transmitting a request signal; request response signalreceiving means for receiving a request response signal transmitted froma receiving station or from a second other relay station, in response tothe request signal transmitted by the request signal transmitting means;interstation communication speed determining means for determining aninterstation communication speed between the host relay station and thereceiving station or the second other relay station as a source of therequest response signal, based on an interference level included in therequest response signal received by the request response signalreceiving means; and request response signal transmitting means fortransmitting a request response signal containing the interference levelmeasured by the interference level measuring means, and the interstationcommunication speed information determined by the interstationcommunication speed determining means, and, where the request responsesignal is one received from the second other relay station, alsocontaining interstation communication speed information included in therequest response signal, to the transmitting station or the other relaystation as a source of the request signal.

A program for the relay station according to the present invention maybe a program applied to a multihop mobile communication system and, forrelaying transmission of a packet from a transmitting station to areceiving station, letting a computer execute: a request signalreceiving step of receiving a request signal transmitted from thetransmitting station or from another relay station; an interferencelevel measuring step of measuring an interference level at the hostrelay station when a request signal is received in the request signalreceiving step; a request signal transmitting step of transmitting arequest signal; a request response signal receiving step of receiving arequest response signal transmitted from the receiving station or from asecond other relay station, in response to the request signaltransmitted in the request signal transmitting step; an interstationcommunication speed determining step of determining an interstationcommunication speed between the host relay station and the receivingstation or the second other relay station as a source of the requestresponse signal, based on an interference level included in the requestresponse signal received in the request response signal receiving step;and a request response signal transmitting step of transmitting arequest response signal containing the interference level measured inthe interference level measuring step, and the interstationcommunication speed information determined in the interstationcommunication speed determining step, and, where the request responsesignal is one received from the second other relay station, alsocontaining interstation communication speed information included in therequest response signal, to the transmitting station or the other relaystation as a source of the request signal.

In the case of the relay station according to the present invention (orthrough execution of the relay station program), the relay stationmeasures the interference level at the relay station itself whenreceiving a request signal having been transmitted from the transmittingstation or from another relay station, and transmits a request responsesignal containing the measured interference level to the transmittingstation or the relay station as a source of the request signal. Therelay station transmits the request signal and determines theinterstation communication speed between the relay station and thereceiving station or second other relay station as a source of therequest response signal, based on the interference level included in therequest response signal to the request signal. Then the relay stationputs the interstation communication speed information about theinterstation communication speed thus determined, into a requestresponse signal and transmits the request response signal to thetransmitting station or the relay station as a source of the requestsignal. This permits the relay station to transmit the information aboutthe interstation communication speed between each pair of stationsconstituting a communication path between the transmitting station andthe receiving station, to the transmitting station, whereby thetransmitting station is able to determine the total communication speedbetween the transmitting station and the receiving station on the basisof the interstation communication speed between each pair of stationsand to determine the communication path with the largest communicationspeed or the communication path satisfying the required line quality onthe basis of the communication speed.

Another relay station according to the present invention is a relaystation comprising: request signal receiving means for receiving arequest signal transmitted from a transmitting station or from anotherrelay station; interference level measuring means for measuring aninterference level at the host relay station when the request signalreceiving means receives a request signal; interstation communicationspeed determining means for determining an interstation communicationspeed between the host relay station and the transmitting station or theother relay station as a source of the request signal, based on theinterference level measured by the interference level measuring means;request signal transmitting means for transmitting a request signal;request response signal receiving means for receiving a request responsesignal transmitted from a receiving station or from a second other relaystation, in response to the request signal transmitted by the requestsignal transmitting means; and request response signal transmittingmeans for transmitting a request response signal containing theinterstation communication speed information determined by theinterstation communication speed determining means, and interstationcommunication speed information included in the request response signalreceived by the request response signal receiving means, to thetransmitting station or the other relay station as a source of therequest signal.

A program for the relay station according to the present invention is aprogram applied to a multihop mobile communication system and, forrelaying transmission of a packet from a transmitting station to areceiving station, letting a computer execute: a request signalreceiving step of receiving a request signal transmitted from thetransmitting station or from another relay station; an interferencelevel measuring step of measuring an interference level at the hostrelay station when a request signal is received in the request signalreceiving step; an interstation communication speed determining step ofdetermining an interstation communication speed between the host relaystation and the transmitting station or the other relay station as asource of the request signal, based on the interference level measuredin the interference level measuring step; a request signal transmittingstep of transmitting a request signal; a request response signalreceiving step of receiving a request response signal transmitted fromthe receiving station or from a second other relay station, in responseto the request signal transmitted in the request signal transmittingstep; and a request response signal transmitting step of transmitting arequest response signal containing the interstation communication speedinformation determined in the interstation communication speeddetermining step, and interstation communication speed informationincluded in the request response signal received in the request responsesignal receiving step, to the transmitting station or the other relaystation as a source of the request signal.

The relay station according to the present invention (the relay stationprogram as executed) measures the interference level at the relaystation itself when receiving a request signal having been transmittedfrom the transmitting station or from another relay station, anddetermines the interstation communication speed between the relaystation and the transmitting station or the relay station as a source ofthe request signal on the basis of the measured interference level. Thenthe relay station puts the interstation communication speed informationabout the interstation communication speed thus determined, into arequest response signal and transmits it to the transmitting station.This permits the relay station to transmit the information about theinterstation communication speed between each pair of stationsconstituting a communication path between the transmitting station andthe receiving station, to the transmitting station, whereby thetransmitting station is able to determine the total communication speedbetween the transmitting station and the receiving station on the basisof the interstation communication speed between each pair of stationsand to determine the communication path with the largest communicationspeed or the communication path satisfying the required line quality onthe basis of the communication speed.

Another relay station according to the present invention is a relaystation comprising: request signal receiving means for receiving arequest signal transmitted from a transmitting station or from anotherrelay station; interference level measuring means for measuring aninterference level at the host relay station when the request signalreceiving means receives a request signal; interstation communicationspeed determining means for determining an interstation communicationspeed between the host relay station and the transmitting station or theother relay station as a source of the request signal, based on theinterference level measured by the interference level measuring means;and request signal transmitting means for transmitting a request signalcontaining the interstation communication speed information determinedby the interstation communication speed determining means, and, wherethe request signal is one received from the other relay station, alsocontaining interstation communication speed information included in therequest signal.

A program for the relay station according to the present invention is aprogram applied to a multihop mobile communication system and, forrelaying transmission of a packet from a transmitting station to areceiving station, letting a computer execute: a request signalreceiving step of receiving a request signal transmitted from thetransmitting station or from another relay station; an interferencelevel measuring step of measuring an interference level at the hostrelay station when a request signal is received in the request signalreceiving step; an interstation communication speed determining step ofdetermining an interstation communication speed between the host relaystation and the transmitting station or the other relay station as asource of the request signal, based on the interference level measuredin the interference level measuring step; and a request signaltransmitting step of transmitting a request signal containing theinterstation communication speed information determined in theinterstation communication speed determining step and, where the requestsignal is one received from the other relay station, also containinginterstation communication speed information included in the requestsignal.

The relay station according to the present invention (the relay stationprogram as executed) measures the interference level at the relaystation itself when receiving a request signal having been transmittedfrom the transmitting station or from another relay station, anddetermines the interstation communication speed between the relaystation and the transmitting station or the other relay station as asource of the request signal on the basis of the measured interferencelevel. Then the relay station puts the interstation communication speedinformation about the interstation communication speed thus determined,into a request signal and transmits the request signal to the receivingstation. This permits the relay station to transmit the informationabout the interstation communication speed between each pair of stationsconstituting a communication path between the transmitting station andthe receiving station, to the receiving station, whereby the receivingstation is able to determine the total communication speed between thetransmitting station and the receiving station on the basis of theinterstation communication speed between each pair of stations and todetermine the communication path with the largest communication speed orthe communication path satisfying the required line quality on the basisof the communication speed. Then the receiving station transmits theinformation about the determined communication path to the transmittingstation, whereby the transmitting station can transmit a packet to thereceiving station in accordance with the determined communication path.

In addition to the above mobile communication systems, the presentinvention further provides the mobile communication system wherein thereceiving station and relay station comprise: request signal receivingmeans for receiving a request signal transmitted from the transmittingstation through a communication path with an intermediary of at leastone relay station or through a communication path without anintermediary of a relay station; interference level measuring means formeasuring an interference level at the host station when the requestsignal receiving means receives a request signal; and communicationpropriety determining means for memorizing either of a receiving-stationtarget value and a relay-station target value for control oftransmission power independently set at the receiving station and at therelay station; wherein the communication propriety determining means ofthe receiving station determines whether it is possible to performcommunication requested by a request signal, based on the interferencelevel measured by the interference level measuring means and based onthe receiving-station target value, and the communication proprietydetermining means of the relay station determines whether it is possibleto perform communication requested by a request signal, based on theinterference level and the relay-station target value; and wherein thecommunication path determining means determines a communication path onthe basis of proprieties of the communications determined by therespective communication propriety determining means.

The invention also provides the mobile communication system wherein theinterstation communication speed determining means memorizes areceiving-station target value and a relay-station target value forcontrol of transmission power independently set at the receiving stationand at the relay station and determines the interstation communicationspeed, based on the interference levels at the respective stationsconstituting the communication path, the receiving-station target value,and the relay-station target value.

In these mobile communication systems, the base-station target value isset to the minimum necessary value and the relay-station target value toone different therefrom, whereby it is feasible to suppress the decreaseof system capacity while lowering the error rate of the entire system.

In addition to the aforementioned transmitting stations, the presentinvention further provides the transmitting station wherein thecommunication path determining means memorizes a receiving-stationtarget value and a relay-station target value for control oftransmission power independently set at the receiving station and at therelay station, and determines the communication path with the largestcommunication speed or the communication path satisfying the requiredline quality, based on the interference levels of the respective signalsreceived at the relay station constituting the communication path and atthe receiving station, the receiving-station target value, and therelay-station target value.

Furthermore, the invention provides the transmitting station wherein theinterstation communication speed determining means memorizes areceiving-station target value and a relay-station target value forcontrol of transmission power independently set at the receiving stationand at the relay station, and determines the interstation communicationspeed, based on the interference level at the receiving station or therelay station as a source of the request response signal, thereceiving-station target value, and the relay-station target value.

According to these transmitting stations, it is feasible to suppress thedecrease of system capacity while lowering the error rate of the entiresystem.

In addition to the aforementioned receiving stations, the presentinvention further provides the receiving station wherein thecommunication propriety determining means memorizes a receiving-stationtarget value for control of transmission power set independently of therelay station, and determines whether it is possible to perform thecommunication at the communication speed included in the request signal,based on the interference level and the receiving-station target value.

Furthermore, in addition to the aforementioned relay stations, thepresent invention provides the relay station wherein the communicationpropriety determining means memorizes a relay-station target value forcontrol of transmission power set independently of the receiving stationfor performing packet transmission, and determines whether it ispossible to perform the communication at the communication speedincluded in the request signal, based on the interference level and therelay-station target value.

The present invention also provides the relay station wherein theinterstation communication speed determining means memorizes arelay-station target value for control of transmission power setindependently of the receiving station for performing packettransmission, and determines the interstation communication speed, basedon the interference level and the relay-station target value.

According to each of these stations, it is feasible to suppress thedecrease of system capacity while lowering the error rate of the entiresystem.

In addition to the aforementioned communication path determiningmethods, the present invention further provides the communication pathdetermining method wherein the communication path determining step is todetermine the communication path with the largest communication speed orthe communication path satisfying the required line quality, based onthe interference levels of the respective signals received at the relaystation and at the receiving station, and based on a receiving-stationtarget value and a relay-station target value for control oftransmission power independently set at the receiving station and at therelay station.

According to this communication path determining method, it is feasibleto suppress the decrease of system capacity while lowering the errorrate of the entire system.

In addition to the aforementioned communication path determiningprograms, the present invention further provides the communication pathdetermining program wherein the communication path determining step isto determine the communication path with the largest communication speedor the communication path satisfying the required line quality, based onthe interference levels of the respective signals received at the relaystation and at the receiving station, and based on a receiving-stationtarget value and a relay-station target value for control oftransmission power independently set at the receiving station and at therelay station.

The invention also provides a communication path control program appliedto a multihop mobile communication system and, for relaying transmissionof a packet from a transmitting station to a receiving station, lettinga computer execute: a request signal receiving step of receiving arequest signal transmitted from the transmitting station through acommunication path with an intermediary of at least one relay station orthrough a communication path without an intermediary of a relay station;an interference level measuring step of measuring an interference levelat a host station when a request signal is received in the requestsignal receiving step; a communication propriety determining step ofdetermining whether it is possible to perform communication at acommunication speed included in the request signal, based on theinterference level measured in the interference level measuring step andbased on a relay-station target value for control of transmission powerset independently of the receiving station; and a request responsesignal transmitting step of transmitting a request response signalcontaining information on propriety of communication determined in thecommunication propriety determining step, through the communication pathto the transmitting station.

The invention also provides the communication path control programwherein an interstation communication speed determining step is todetermine an interstation communication speed, based on the interferencelevel and the relay-station target value for control of transmissionpower set independently of the receiving station.

When these programs are executed by the computer, as in the case of thecommunication path determining methods, it is feasible to suppress thedecrease of system capacity while lowering the error rate of the entiresystem.

The above object and other features and advantages of the presentinvention will become apparent to those skilled in the art by readingthe following detailed description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing a configuration of a mobilecommunication system according to an embodiment.

FIG. 2 is an illustration showing a configuration of a mobilecommunication system according to an embodiment.

FIG. 3 is an illustration showing a configuration of a mobile stationaccording to an embodiment.

FIG. 4 is an illustration showing a configuration of a relay stationaccording to an embodiment.

FIG. 5 is an illustration showing a configuration of a base stationaccording to an embodiment.

FIG. 6 is an illustration showing an example of radio link design in amobile communication system according to an embodiment.

FIG. 7A is an illustration to illustrate communication speeds in singlehop connection. FIG. 7B is an illustration to illustrate communicationspeeds in multihop connection.

FIG. 8 is a flowchart showing the operation of a communication pathdetermining method according to an embodiment.

FIG. 9 is a flowchart showing the operation of a communication pathdetermining method according to an embodiment.

FIG. 10A is an illustration to illustrate a relaying system by multihopconnection. FIG. 10B is an illustration to illustrate another relayingsystem by multihop connection.

FIG. 11 is a flowchart showing the operation of a communication pathdetermining method according to an embodiment.

FIG. 12 is a flowchart showing the operation of a communication pathdetermining method according to an embodiment.

FIG. 13 is an illustration showing a configuration of a mobile stationaccording to an embodiment.

FIG. 14 is an illustration showing a configuration of a relay stationaccording to an embodiment.

FIG. 15 is an illustration showing a configuration of a base stationaccording to an embodiment.

FIG. 16 is a flowchart showing the operation of a communication pathdetermining method according to an embodiment.

FIG. 17A is an illustration showing a configuration of a computerprogram for the transmitting station according to an embodiment. FIG.17B is an illustration showing a configuration of a computer program forthe relay station according to an embodiment. FIG. 17C is anillustration showing a configuration of a computer program for thereceiving station according to an embodiment.

FIG. 18A is an illustration showing a configuration of another computerprogram for the transmitting station according to an embodiment. FIG.18B is an illustration showing a configuration of another computerprogram for the relay station according to an embodiment. FIG. 18C is anillustration showing a configuration of another computer program for thereceiving station according to an embodiment.

FIG. 19 is an illustration showing another example of a receivingstation program.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the mobile communication system accordingto the present invention will be described below in detail withreference to the drawings. It is noted that the same reference symbolswill denote the same elements throughout the description of thedrawings, without redundant description thereof.

First Embodiment Outline of Entire Mobile Communication System

FIG. 1 is an illustration showing the configuration of mobilecommunication system 1 according to the present embodiment. As shown inFIG. 1, mobile communication system 1 of the first embodiment iscomprised of mobile station 10, at least one relay station 30, and basestation 20. The description herein will be given on the assumption thatthe “transmitting station” is mobile station 10 such as a cell phoneowned by a user and the “receiving station” is base station 20 that canbe connected to another base station 20 through a core network, but itis noted that the transmitting station can be base station 20 and thereceiving station mobile station 10 or that the transmitting station canbe one of relay stations 30. Relay station 30 is a terminal (relayterminal) having a function of relaying a packet from mobile station 10to base station 20 or relaying a packet from base station 20 to mobilestation 10. Since this relay station 30 consumes power for packetrelaying, it is considered to be a terminal capable of receiving supplyof power from a solar cell or a power generator, or through a wire, inaddition to terminal equipment powered by the conventional battery.Conceivable examples of relay station 30 include those installed by atelecommunications carrier for the purpose of reduction of cost in placeof base stations 20 to cover areas, those receiving supply ofelectricity with movement like automobiles and trains, those fixed andreceiving supply of power like vending machines, and so on. Namely,relay station 30 corresponds to equipment having the function of mobilestation 10 and the relaying function, and to relaying apparatusinstalled on such vehicles as automobiles, trains, and the like and onvending machines.

Incidentally, in the present system base station 20 need secure aconnection with mobile station 10 directly or via at least one relaystation 30. For this reason, each base station 20 updates and retains atevery predetermined interval of time, not only affiliation informationof mobile station 10 capable of direct communication, but alsoaffiliation information of relay station 30 capable of directcommunication and affiliation information of mobile station 10 incapableof direct communication but capable of communication via relay station30. This enables base station 20 to retain the affiliation informationof all mobile stations 10 capable of direct and indirect communication,whereby connection is secured between base station 20 and all the mobilestations 10 capable of indirect and direct communication.

Each of mobile station 10 and relay station 30 spreads and transmits arequest signal with information of its own ID at every predeterminedinterval of time, in order to secure a connection path to base station20. Every station receiving a request signal transmits a requestresponse signal to the request signal. The request response signalcontains relay information (e.g., containing information such as an IDof the source station, an ID of mobile station 10 having transmitted theoriginal request signal, an interference level at the source station, ahop count and a communication speed to base station 20, and so on).Mobile station 10, receiving a request response signal, determines aconnection path from the information in the signal, transmits an ACKsignal to a station to be connected, and establishes the connectionpath.

For example, mobile station 10 shown in FIG. 2, spreads and transmitsthe request signal in order to secure a connection path to base station20. A dotted circle represents a range of arrival of the request signalfrom mobile station 10, and each relay station 30 existing in the rangeof arrival, when receiving the request signal, transmits a requestresponse signal accompanied by the relay information. Then mobilestation 10, receiving this request response signal, determines aconnection path from the relay information of the request responsesignal, transmits an ACK signal to a station to be connected (e.g.,relay station 30), and establishes the connection path (mobile station10-relay station 30-base station 20).

The configurations of mobile station 10, base station 20, and relaystation 30 constituting the present system will be described below withfocus on portions associated with the present invention.

[About Mobile Station]

The configuration of mobile station 10 will be described below referringto FIG. 3. As shown in FIG. 3, mobile station 10 is comprised oftransmitted data processor 13 for processing input data and transmittingthe processed data; received data processor 12 for processing a receivedsignal and converting the processed data into output data; requestsignal transmitter 11 a for transmitting a request signal; requestresponse signal receiver 11 b for receiving a request response signal toa request signal; and signal analyzer 11 c. Here the request signaltransmitter 11 a, request response signal receiver 11 b, and signalanalyzer 11 c constitute communication path determiner 11 fordetermining a communication path.

Request signal transmitter 11 a has a function of transmitting a requestsignal containing an ID for identifying the host station and informationabout a request communication speed. Request signal transmitter 11 atransmits the request signal on a regular basis or at timing ofcommunication.

Request response signal receiver 11 b has a function of receiving arequest response signal transmitted in response to a request signal. Arequest response signal received is fed into signal analyzer 11 c.

Signal analyzer 11 c has a function of analyzing an input requestresponse signal and determining whether it is possible to performcommunication with base station 20 through a predetermined communicationpath on the basis of communication propriety information included in therequest response signal. It further has a function of giving aninstruction about whether request signal transmitter 11 a shouldtransmit a request signal, based on the result of the determination.

Mobile station 10 may also include a channel group selector forselecting a channel group, a hop count information buffer for memorizinginformation of a hop count, and so on.

[About Relay Station]

In the present embodiment, relay station 30 is not a terminalfunctioning as a repeater for relaying a spread signal received as itis, but a terminal having capability of despreading signals receivedfrom a plurality of mobile stations 10 or base stations 20 and decodingthem into information sequences. Relay station 30 calculatestransmission powers according to desired reception levels notified of bystations to receive packets (packet receivers), again spreads theinformation sequences, assigns the calculated transmission powers to therespective spread sequences independently of each other, and places andtransmits the spread information sequence signals on predeterminedchannels (e.g., channels according to channel groups selected based onhop counts to base station 20).

Since the relay station has the function of calculating a transmissionpower according to a desired reception level of a packet receiver, itcan implement stable and reliable transmission using the transmissionpower. Since relay station 30 despreads a received signal once anddecodes it into an information sequence (to be spread), it is feasibleto effect a correction for gain of the signal.

The configuration of relay station 30 will be described below referringto FIG. 4. As shown in FIG. 4, relay station 30 is comprised of requestsignal receiver 31 for receiving a request signal; request signaltransmitter 32 for transmitting a request signal; request responsesignal receiver 33 for receiving a request response signal transmittedin response to a request signal; request response signal transmitter 34for transmitting a request response signal to a request signal receivedby request signal receiver 31; data processor 35 for processing packetdata; interference level measuring part 36 for measuring an interferencelevel at the host station; and communication propriety determiner 37 fordetermining whether it is possible to perform communication requested bya request signal.

Data processor 35 extracts a desired signal from a received signal anddespreads it to reproduce information. The reproduced informationsequence is again subjected to coding, spreading, and D/A conversion andthe resultant data is transmitted as placed on a carrier wave amplifiedaccording to a transmission power level calculated from information(e.g., information about an interference level and a propagation loss ata packet receiver, or the like) acquired from a transmission powercontroller (not shown).

Request signal receiver 31 has a function of receiving a request signaltransmitted from mobile station 10 or from another relay station 30. Anotification of reception of a request signal at request signal receiver31 is fed into interference level measuring part 36.

Interference level measuring part 36 has a function of measuring aninterference level at the host station at the time of receiving arequest signal.

Communication propriety determiner 37 has a function of determiningwhether it is possible to perform communication at a communication speedrequested by a request signal received by request signal receiver 31,based on an interference level measured by interference level measuringpart 36. Whether it is possible to perform communication at acommunication speed requested is determined, for example, by finding amaximum communication speed available for communication on the basis ofthe interference level measured by interference level measuring part 36and comparing it with the communication speed requested by the requestsignal. The result of the determination by communication proprietydeterminer 37 is fed into request response signal transmitter 34. Whenthe determination is that it is possible to perform the communication,request signal transmitter 32 is notified of the determination result.

Request signal transmitter 32 has a function of transmitting a requestsignal when receiving a notification of the determination of beingcommunicable from communication propriety determiner 37.

Request response signal receiver 33 has a function of receiving arequest response signal transmitted in response to a request signaltransmitted by request signal transmitter 32.

Request response signal transmitter 34 has a function of putting thedetermination propriety information based on the result of thedetermination by communication propriety determiner 37, into a requestresponse signal and transmitting the request response signal. It alsohas a function of, when request response signal receiver 33 receives arequest response signal, putting the communication propriety informationincluded in the received request response signal, into a requestresponse signal and transmitting the request response signal. Thedestination of the request response signal is relay station 30 or mobilestation 10 being a source of a request signal, and the destination isspecified by an ID included in the request signal.

[About Base Station]

The configuration of base station 20 will be described below referringto FIG. 5. As shown in FIG. 5, base station 20 is comprised oftransmitted data processor 25 for processing transmitted data from thecore network and transmitting the processed data; received dataprocessor 24 for processing received data and generating received datato be transmitted to the core network; request signal receiver 21 forreceiving a request signal; interference level measuring part 22 formeasuring an interference level at receiving station 20; communicationpropriety determiner 26 for determining whether it is possible toperform communication with mobile station 10 on the basis of theinterference level measured by interference level measuring part 22; andrequest response signal transmitter 23 for transmitting a requestresponse signal containing communication propriety informationdetermined by communication propriety determiner 26.

Request signal receiver 21 has a function of receiving a request signaltransmitted from relay station 30 or from mobile station 10 andsupplying a notification of reception of the request signal tointerference level measuring part 22.

Interference level measuring part 22 has a function of measuring aninterference level at receiving station 20 when receiving a notificationof reception of a request signal from request signal receiver 21.

Communication propriety determiner 26 has a function of determiningwhether it is possible to perform communication at a requestcommunication speed included in a request signal received by requestsignal receiver 21. Whether it is possible to perform communication at arequest communication speed is determined, for example, by finding amaximum communication speed available for communication on the basis ofthe interference level measured by interference level measuring part 22and comparing it with the request communication speed requested by therequest signal.

Request response signal transmitter 23 has a function of transmitting arequest response signal containing communication propriety informationon propriety of communication based on the determination bycommunication propriety determiner 26, to relay station 30 or mobilestation 10 as a source of a request signal. Request response transmitter23 can identify relay station 30 or transmitting station 10 as a sourceof the request signal, based on a source ID included in the requestsignal.

[Method of Determining Communication Path]

Methods of determining a communication path in mobile communicationsystem 1 of the present embodiment will be described below, while alsodetailing the communication path determining method according to anembodiment of the present invention. The methods of determining thecommunication path include methods of determining a communication pathwith a largest communication speed and methods of determining acommunication path satisfying a required line quality. These methodswill be described below using examples in which mobile station 10 servesas a transmitting station.

Prior to the description of the communication path determining methods,an example of radio link design in the present system is presented inFIG. 6. Referring to FIG. 6, the cell radius in this system is 1.66 kmand communication at 64 kbps is secured in single hop connection. Inthis system communication at 384 kbps is available in part inside thecell where the distance is 1.06 km from base station 20. When multihopconnection with a single relay is applied in this system, the presentsystem permits four communication modes of single hop 384 kbps, multihop384 kbps, single hop 64 kbps, and multihop 64 kbps. Supposing a relay ata relay station requires a double communication time, an effectivecommunication speed in multihop connection becomes half that in singlehop connection. Namely, the effective communication speed is 192 kbps in384 kbps multihop connection, and 32 kbps in 64 kbps multihopconnection. This point will be detailed below. FIG. 7A shows an examplein which mobile stations 10 are connected to a base station 20 by singlehop connection; a mobile station 10 within 1.06 km from the base station20 can be connected at 384 kbps, while another mobile station 10 apartmore than 1.06 km from the base station within the cell is connected at64 kbps. FIG. 7B is an illustration showing an example in which a mobilestation 10 located more than 1.06 km apart from the base station 20 isconnected by multihop connection. Since a relay station 30 for relayingbetween the mobile station 10 and the base station 20 is located within1.06 km from the base station 20, a connection at 384 kbps is possiblebetween the relay station 30 and the base station 20. If the mobilestation 10 and relay station 30 are located within 1.06 km, a connectionat 384 kbps is also possible between the mobile station 10 and the relaystation 30. Supposing the relay requires double the communication time,the multihop connection shown in FIG. 7B permits communication at 192kbps between the mobile station 10 and the base station 20.

Methods of determining the communication path with the largestcommunication speed will be described below with reference to FIG. 8.The methods of searching for the communication path with the largestcommunication speed include methods of sequentially searching for it,starting from the communication path with the maximum availablecommunication speed and methods of sequentially searching for it,starting from the communication path with the minimum availablecommunication speed, among which a method of sequentially searching forthe communication path, starting from the communication path with themaximum available communication speed will be first described. FIG. 8 isa flowchart showing the operation of communication path determiner 11 indetermining the communication path with the largest communication speed.

Mobile station 10 determines the communication mode and communicationpath at predetermined intervals of time or at timing when a need forcommunication arises. As shown in FIG. 8, the mobile station firstattempts to connect by 384 kbps single hop connection (S11).Specifically, mobile station 10 makes request signal transmitter 11 atransmit a request signal containing a communication connection requestat 384 kbps and, when base station 20 receives the request signaltransmitted from mobile station 10, interference level measuring part 22measures the interference level at base station 20. Subsequently, basestation 20 makes communication propriety determiner 26 determine whetherit is possible to perform the communication at 384 kbps with mobilestation 10, based on the measured interference level. Then base station20 puts communication propriety information on propriety ofcommunication thus determined, into a request response signal andtransmits the request response signal to mobile station 10. Thereafter,mobile station 10, receiving the request response signal, makes signalanalyzer 11 c analyze the communication propriety information includedin the request response signal. As a consequence, if the single hopcommunication at 384 kbps is possible, a communication path by 384 kbpssingle hop connection is determined and the communication is started.

If it is impossible to perform the communication by 384 kbps single hopconnection, a search is made for a relay station 30 available for 384kbps multihop communication (S12). Specifically, mobile station 10transmits a request signal containing a communication connection requestat 384 kbps and, when a relay station 30 receives the request signaltransmitted from mobile station 10, the relay station 30 measures theinterference level at the relay station itself. Then the relay station30 makes communication propriety determiner 37 determine whether it ispossible to perform the communication at the communication speed (384kbps herein) requested by the request signal, based on the measuredinterference level. When the result of the determination is that it isimpossible to perform the communication, the relay station 30 puts thecommunication propriety information indicating the incapability of thecommunication, into a request response signal and transmits it to mobilestation 10. In this case, request signal transmitter 32 transmits norequest signal. Namely, since it is impossible for this relay station 30to perform the communication at the request communication speed, it isuseless to perform a search for a communication path from this relaystation 30 to base station 20. For this reason, transmission of therequest signal is terminated at the point of the determination ofincapability of communication, thereby achieving increase of efficiencyof the entire mobile communication system. When communication proprietydeterminer 37 determines that it is possible to perform thecommunication, the relay station 30 transmits a request signalcontaining a communication connection request at 384 kbps. When basestation 20 receives the request signal transmitted from the relaystation 30, interference level measuring part 22 measures theinterference level at the base station and communication proprietydeterminer 26 determines whether it is possible to perform thecommunication at the request communication speed with the mobilestation, based on the measured interference level. Subsequently, basestation 20 makes request response signal transmitter 23 transmit arequest response signal containing the communication proprietyinformation on propriety of communication to the relay station 30 as asource of the request signal. The relay station 30, receiving therequest response signal thus transmitted, transmits a request responsesignal containing the communication propriety information included inthe received request response signal and the communication proprietyinformation at the relay station itself (“communicable” herein), tomobile station 10.

Then mobile station 10, receiving the request response signal, makessignal analyzer 11 c analyze the communication propriety informationincluded in the request response signal. As a consequence, if thecommunication by 384 kbps multihop connection is possible, that is, whenthe relay station 30 and base station 20 both are communicable, themobile station determines the communication path by 384 kbps multihopconnection and starts the communication.

If the communication by 384 kbps multihop connection is impossible, themobile station attempts to connect by 64 kbps single hop connection(S13). A specific method is the same as the aforementioned attempt onthe 384 kbps single hop connection. When it is possible to perform thecommunication by 64 kbps single hop connection, the mobile stationdetermines the communication path by 64 kbps single hop connection andstarts the communication. When it is impossible to perform thecommunication by 64 kbps single hop connection, the mobile stationattempts to connect by 64 kbps multihop connection (S14). A specificmethod is the same as the aforementioned attempt on the 384 kbpsmultihop connection. When it is possible to perform the communication by64 kbps multihop connection, the mobile station determines thecommunication path by 64 kbps multihop connection and starts thecommunication. When it is impossible to perform the communication by 64kbps multihop connection, the mobile station is incapable of anycommunication and the mobile station like a cell phone or the like isdetermined to be located outside the communication area.

As described above, mobile station 10 sequentially attempts to connectfrom the fastest communication speed and establishes a connection tobase station 20 at the communication speed determined as communicable,whereby it is feasible to determine the communication path with thelargest communication speed and establish the connection between mobilestation 10 and base station 20.

A method of sequentially performing the search from the communicationpath with the minimum communication speed will be described below. FIG.9 is a flowchart showing the operation of communication path determiner11 in determining a communication path with a largest communicationspeed. It is assumed that the conditions for radio link design are thesame as those in FIG. 6 and mobile communication system 1 permits thecommunication speeds of 384 kbps and 64 kbps in each of the single modeand the multimode. As shown in FIG. 9, mobile station 10 first attemptsto connect by 64 kbps multihop connection in which it is easy to securecommunication (S21). A specific method is the same as the aforementionedattempt on the 64 kbps multihop connection. When it is possible toperform the communication by 64 kbps multihop connection, the mobilestation attempts to connect by 64 kbps single hop connection, whilesecuring the 64 kbps multihop connection (S23). When the first attemptresults in finding incapability of the communication by 64 kbps multihopconnection, the mobile station also attempts to connect by 64 kbpssingle hop connection (S22), because there is a possibility that thefailure in connection occurred because of the absence of an appropriaterelay station 30. When this attempt results in finding incapability ofthe communication by 64 kbps single hop connection, the mobile stationbecomes incapable of any communication.

When it is possible to perform the communication by 64 kbps single hopconnection, the mobile station attempts to connect by 384 kbps multihopconnection, while securing the communication by 64 kbps single hopconnection (S24). When it is possible to perform the communication by384 kbps multihop connection, the mobile station attempts to connect by384 kbps single hop connection, while securing the communication by 384kbps multihop connection (S26). When it is impossible to perform thecommunication by 384 kbps single hop connection, the mobile stationstarts communication at the maximum of communication speeds succeeded inestablishment of communication heretofore, i.e., the communication by384 kbps multihop connection (effective communication speed of 192kbps). When it is possible to perform the communication by 384 kbpssingle hop connection, the mobile station starts the communication by384 kbps single hop connection.

When at step S24 it is impossible to perform the communication by 384kbps multihop connection, there is also a possibility that the failurein connection occurred because of the absence of an appropriate relaystation 30, and thus the mobile station also attempts to connect by 384kbps single hop connection (S25). In this case, where it is impossibleto perform the communication by 384 kbps single hop connection, themobile station starts the communication at the maximum of communicationspeeds succeeded in establishment of communication heretofore, namely,the communication by 64 kbps single hop connection. When step S25results in succeeding in the 384 kbps single hop connection, the mobilestation determines the communication path by 384 kbps single hopconnection and starts the communication.

Since the search is started from the communication path with the minimumcommunication speed easy for securement of communication as describedabove, the time to the start of communication can be kept as short aspossible, by first securing the communication path, and thecommunication path with the largest communication speed can bedetermined by performing the search for the communication path whilestepwise increasing the communication speed.

A method of determining the communication path satisfying the requiredline quality will be described next. Prior to the description of thecommunication path determining method, let us describe the line qualityand others exemplified in the description.

The required line quality herein is defined by communication speeds,values of which are four values of 1 Mbps, 2 Mbps, 4 Mbps, and 8 Mbps,and communication modes corresponding thereto are 1, 2, 4, and 8 Mbpsmultihop and single hop communication modes. In the above-describedmultihop connection a relay required double the communication time, buthere is also described a case where the relay rarely causes the delay ofthe communication time. Since these two cases occur depending uponsystems of multihop relay station 30 as described below, which flowshould be adopted is determined according to the system of relay station30. The multihop relay systems will be described below. The firstmultihop system, as shown in FIG. 10A, is a system in which the relaystation performs no relay transmission during reception of packet. Inthis case, therefore, supposing a time necessary for transmission of Npackets in single hop communication is Tn, a time necessary for packettransmission in multihop communication is 2×Tn. Namely, thecommunication speed during multihop communication is half thecommunication speed during single hop communication. The second multihopsystem, as shown in FIG. 10B, is a system in which the relay stationalso performs relay transmission during reception of packet. In thiscase relay station 30 transmits the (n−1)th packet during reception ofthe nth packet, so that the time for transmission of N packets is equalto the time necessary for transmission of (N+1) packets. In the formersystem, where the line quality request is one for k Mbps, thecommunication speed satisfying the request is k Mbps in single hopconnection and 2 k Mbps in multihop connection. In the latter system,where the line quality request is one for k Mbps, the communicationspeed satisfying the request is k Mbps both in single hop connection andin multihop connection.

The operation of a communication path determining method in the formermultihop system will be described with reference to FIG. 11. When therequired line quality is given as a communication speed (S30), mobilestation 10 first attempts to make a single hop connection at the givencommunication speed (S31, S33, S35, or S37). For example, where therequired line quality is 2 Mbps, the mobile station attempts to connectby 2 Mbps single hop connection (S33). Specifically, mobile station 10transmits a request signal containing a communication connection requestat the given communication speed and, when base station 20 receives therequest signal transmitted from mobile station 10, interference levelmeasuring part 22 measures the interference level at base station 20.Subsequently, based on the measured interference level, communicationpropriety determiner 26 determines whether it is possible to perform thecommunication with mobile station 10 at the communication speedrequested by the request signal. Then base station 20 puts thecommunication propriety information based on the determination, into arequest response signal and transmits it to mobile station 10. Mobilestation 10, receiving the request response signal, then determineswhether it is possible to perform the single hop communication at thegiven communication speed, based on the communication proprietyinformation included in the request response signal. When it is possibleto perform the single hop communication at the given communicationspeed, the mobile station determines the communication path and startsthe communication. When it is impossible to perform the single hopcommunication at the given communication speed, the mobile stationattempts to make a multihop connection at a communication speed equal todouble the given communication speed (S32, S34, or S36). For example,where 2 Mbps is given as the requested line quality, the mobile stationattempts to connect by 4 Mbps multihop connection (S34). Specifically,mobile station 10 transmits a request signal containing a communicationconnection request at the communication speed of twice the givencommunication speed and, when a multihop relay station 30 receives therequest signal transmitted from the mobile station 10, the relay station30 measures the interference level at the station itself. Then the relaystation 30 makes communication propriety determiner 37 determine whetherit is possible to perform the communication at the communication speed(4 Mbps herein) requested by the request signal, based on the measuredinterference level. When the result of the determination is that it isimpossible to perform the communication, the relay station 30 puts thecommunication propriety information indicating the incapability of thecommunication, into a request response signal and transmits the requestresponse signal to the mobile station 10. In this case, request signaltransmitter 32 transmits no request signal in order to increase theefficiency of the mobile communication system. When communicationpropriety determiner 37 determines that it is possible to perform thecommunication, the relay station 30 transmits a request signalcontaining a communication connection request at 4 Mbps.

Thereafter, when base station 20 receives the request signal transmittedfrom the relay station 30, interference level measuring part 22 measuresthe interference level at the base station and, based on the measuredinterference level, communication propriety determiner 26 determineswhether it is possible to perform the communication with the mobilestation at the requested communication speed. Subsequently, base station20 makes request response signal transmitter 23 transmit a requestresponse signal containing the communication propriety information onpropriety of communication to the relay station 30 as a source of therequest signal. The relay station 30 receives the request responsesignal and transmits a request response signal containing thecommunication propriety information included in the received requestresponse signal and the communication propriety information at the relaystation (“communicable” herein), to mobile station 10. Then mobilestation 10, receiving the request response signal, determines whether itis possible to perform the multihop communication at the givencommunication speed, based on the communication propriety informationincluded in the request response signal. When it is possible to performthe multihop communication at the given communication speed, that is,when the relay station 30 and base station 20 both are communicable, themobile station determines the communication path by multihop connectionat the communication speed and starts the communication. When it isimpossible to perform the communication at the given communicationspeed, the mobile station is incapable of any communication.

A communication path determining method in the latter system withoutdelay of communication speed will be described below with reference toFIG. 12. First, when the requested line quality is given as acommunication speed, mobile station 10 attempts to connect by single hopconnection at the communication speed (S41, S43, S45, or S47). Forexample, where 2 Mbps is given as the requested line quality, the mobilestation attempts to connect by 2 Mbps single hop connection (S43). Aspecific method of the attempt on connection is the same as the aboveand redundant description is omitted herein.

When it is possible to perform the communication at the givencommunication speed, the mobile station determines the communicationpath in single hop connection at the communication speed and starts thecommunication. When it is impossible to perform the single hopcommunication at the given communication speed, the mobile stationattempts to make a multihop connection at the communication speed (S42,S44, S46, or S48). For example, where 2 Mbps is given as the requestedline quality, the mobile station attempts to connect by 2 Mbps multihopconnection (S44). A specific method of the attempt on connection is thesame as the above and redundant description thereof is omitted herein.When it is possible to perform the multihop communication at thecommunication speed requested by the request signal, the mobile stationdetermines the communication path in multihop connection at thecommunication speed and starts the communication. When it is impossibleto perform the communication at the given communication speed, themobile station is incapable of any communication.

When a requested line quality is given, the mobile station is able todetermine the communication path satisfying the line quality and make aconnection, as described above, and it is thus feasible to provide ahigh-quality communication environment.

When there exist a plurality of communication paths satisfying therequested line quality, a communication path may be determined bynarrowing down communication paths, based on hop counts from mobilestation 10 to base station 20, based on totals of transmission powers atmobile station 10 and at relay station 30, or the like. For example,where the communication speed of 2 Mbps is requested as a line qualityand if the 2 Mbps single hop connection and 4 Mbps multihop connectionboth are available, the 2 Mbps single hop path with the smaller hopcount may be determined as a communication path. Since the presentembodiment adopts the methods of first attempting the single hopconnection, the communication path with the smaller hop count ispreferentially selected.

Second Embodiment

The mobile communication system and communication path determiningmethod of the second embodiment for permitting communication pathdeterminer 11 to determine an optimal communication speed will bedescribed, using an example of the mobile communication system withmultiple relay stations 30. FIG. 13 to FIG. 15 show the configurationsof mobile station 10, relay station 30, and base station 20,respectively, which constitute the mobile communication system accordingto the second embodiment.

[About Mobile Station]

The configuration of mobile station 10 will be first described withreference to FIG. 13. Mobile station 10 is comprised of request signaltransmitter 11 a for transmitting a request signal; request responsesignal receiver 11 b for receiving a request response signal transmittedin response to a request signal; communication speed determiner 11 d fordetermining a communication speed on the basis of a request responsesignal; and communication path selector 11 f for selecting acommunication path on the basis of a communication speed determined bycommunication speed determiner 11 d. These components constitutecommunication path determiner 11. Mobile station 10 is also providedwith connection signal transmitter 14 for transmitting a connectionsignal, and ACK signal receiver 15 for receiving an ACK signaltransmitted in response to a connection signal and is further providedwith transmitted data processor 13 and received data processor 12similar to those in mobile station 10 in the first embodiment.

Request signal transmitter 11 a has a function of transmitting a requestsignal containing an ID for distinguishing the host station. Requestsignal transmitter 11 a transmits the request signal on a regular basisor at timing of communication. After a start of communication, requestsignal transmitter 11 a regularly transmits the request signal.

Request response signal receiver 11 b has a function of receiving arequest response signal transmitted in response to a request signal. Arequest signal received is fed into communication speed determiner 11 d.

Communication speed determiner lid has a function of determining acommunication speed from mobile station 10 to base station 20, based ona request response signal received by request response signal receiver11 b. Communication speed determiner lid has interstation communicationspeed determiner 11 e for determining an interstation communicationspeed between the mobile station and relay station 30 or base station 20as a source of a request response signal on the basis of an interferencelevel at the source of the request response signal included in therequest response signal. Communication speed determiner 11 d determinesthe communication speed from mobile station 10 to base station 20, basedon the interstation communication speed determined by interstationcommunication speed determiner 11 e and based on an interstationcommunication speed between each pair of stations constituting thecommunication path from relay station 30 as a source of the requestresponse signal to base station 20, included in the received requestresponse signal. Where the source of the request response signal is basestation 20, the request response signal contains no information ofinterstation communication speed, and thus the interstationcommunication speed determined by interstation communication speeddeterminer lie is nothing but the communication speed between thetransmitting station and the receiving station. Now, let us describe amethod of determining the communication speed on the basis of theinterference level. The communication speed is normally one of discretevalues determined depending upon chip rates and thus, for example, thecommunication speed R can be determined as a maximum satisfying thefollowing expression for SIR value S determined by the interferencelevel.R<S×k(constant)

Communication path selector 11 f has a function of determining acommunication path, based on the information of the communication speeddetermined by communication speed determiner 11 d. More specifically, itselects each of a communication path in a single hop connection and acommunication path with a largest communication speed.

[About Relay Station]

Relay station 30 will be described next. In the present embodiment,relay station 30 is similar to relay station 30 in the first embodimentas described above, in that it does not function simply as a repeaterfor relaying spread signals received, as they are.

The configuration of relay station 30 will be described referring toFIG. 14. As shown in FIG. 14, relay station 30 is comprised of requestsignal receiver 31 for receiving a request signal; interference levelmeasuring part 36 for measuring an interference level at the host relaystation 30; request signal transmitter 32 for transmitting a requestsignal; request response signal receiver 33 for receiving a requestresponse signal transmitted in response to a request signal;interstation communication speed determiner 38 for determining aninterstation communication speed between the host relay station 30 andanother relay station 30 or base station 20 as a source of a requestresponse signal on the basis of an interference level included in therequest response signal received by request response signal receiver 33;request response signal transmitter 34 for transmitting a requestresponse signal containing information of the communication speeddetermined by interstation communication speed determiner 38 andinformation of the interference level measured by interference levelmeasuring part 36; and data processor 35 for processing packet data.Relay station 30 is also provided with connection signal receiver 41 forreceiving a connection signal; connection signal transmitter 42 fortransmitting a connection signal; ACK signal receiver 43 for receivingan ACK signal transmitted in response to a connection signal; and ACKsignal transmitter 44 for transmitting an ACK signal.

Data processor 35 extracts a desired signal from a received signal anddespreads it to reproduce information. An information sequencereproduced is again subjected to coding, spreading, and D/A conversionand the resultant data is transmitted on a carrier wave amplifiedaccording to a transmission power level calculated from information(e.g. information about an interference level and a propagation loss ata packet receiver, or the like) acquired from a transmission powercontroller (not shown).

Request signal receiver 31 has a function of receiving a request signaltransmitted from mobile station 10 or from another relay station 30. Anotification indicating reception of a request signal at request signalreceiver 31 is fed into interference level measuring part 36 and intorequest signal transmitter 32.

Interference level measuring part 36 has a function of measuring aninterference level of a request signal at the host relay station 30.

Request signal transmitter 32 has a function of transmitting a requestsignal to another relay station 30 or to base station 20.

Request response signal receiver 33 has a function of receiving arequest response signal transmitted from another relay station 30 orfrom base station 20, in response to a request signal transmitted byrequest signal transmitter 32. A request response signal received is fedinto interstation communication speed determiner 38.

Interstation communication speed determiner 38 has a function ofdetermining an interstation communication speed between the host relaystation and another relay station 30 or base station 20 as a source of arequest response signal, based on the received request response signal.A method of determining the communication speed on the basis of theinterference level is similar to that in the case of mobile station 10.

Request response signal transmitter 34 has a function of transmitting arequest response signal containing information of the interference levelmeasured by the interference level measuring part 36 and theinterstation communication speed determined by interstationcommunication speed determiner 38. The destination of the requestresponse signal is the relay station 30 or mobile station 10 as a sourceof the request signal and the source is specified by an ID included inthe request signal.

[About Base Station]

The configuration of base station 20 will be described below referringto FIG. 15. As shown in FIG. 15, base station 20 is comprised oftransmitted data processor 25 for processing transmitted data from thecore network and transmitting the processed data; received dataprocessor 24 for processing received data and generating received datato be transmitted to the core network; request signal receiver 21 forreceiving a request signal; interference level measuring part 22 formeasuring an interference level at receiving station 20; and requestresponse signal transmitter 23 for transmitting a request responsesignal containing the interference level measured by interference levelmeasuring part 22. Base station 20 is also provided with connectionsignal receiver 27 for receiving a connection signal; and ACK signaltransmitter 28 for transmitting an ACK signal to a connection signal.

Request signal receiver 21 has a function of receiving a request signaltransmitted from relay station 30 or from mobile station 10 andsupplying a notification of reception of a request signal tointerference level measuring part 22.

Interference level measuring part 22 has a function of, when receiving anotification of reception of a request signal from request signalreceiver 21, measuring an interference level at receiving station 20.

Request response signal transmitter 23 has a function of transmittingthe interference level measured by interference level measuring part 22to relay station 30 or mobile station 10 as a source of the requestsignal. Request response signal transmitter 23 is able to specify therelay station 30 or transmitting station 10 as a source, based on thesource ID included in the request signal.

A communication path determining method in mobile communication system 1according to the present embodiment will be described below, while alsodescribing the communication path determining method according to anembodiment with reference to FIG. 16.

FIG. 16 is a flowchart showing the operation of the communication pathdetermining method according to the present embodiment. First, mobilestation 10 transmits a request signal (denoted by “RQ signal” in FIG.16) (S50); base station 20 receives the request signal transmitted frommobile station 10, then measures the interference level at the stationitself, and transmits a request response signal containing the measuredinterference level to mobile station 10 (S52). Mobile station 10,receiving the request response signal transmitted from base station 20,determines the communication speed on the basis of the received requestresponse signal (S54) and transmits a connection notification (denotedby “CN notification” in FIG. 16) containing the information of thedetermined communication speed to base station 20 (S56). Base station20, receiving the connection notification transmitted from mobilestation 10, sends an ACK to mobile station 10 (S58) and a single hopcommunication is established between mobile station 10 and base station20 (S60). This single hop communication is always maintained before anend of the communication between mobile station 10 and base station 20.

Then mobile station 10 again transmits a request signal (S62). Therequest signal transmitted on this occasion is a request signaltransmitted in order to search for a relay station 30A available formultihop communication. In this case, since the communication speed isdetermined later based on the request response signal, the requestsignal does not have to contain the information of the requestcommunication speed. In order to search for a relay station 30A in theneighborhood of mobile station 10, mobile station 10 transmits therequest signal by a transmission power necessary for transmission withina predetermined range. A relay station 30A, receiving the request signaltransmitted from mobile station 10, transmits a request signal (S64).Base station 20, receiving the request signal transmitted from the relaystation 30A, measures the interference level at the station itself andtransmits a request response signal containing the measured interferencelevel to the relay station 30A (S66). The relay station 30A, receivingthe request response signal transmitted from base station 20, determinesan interstation communication speed between the relay station and basestation 20, based on the received request response signal (S68). Therelay station 30A measures the interference level at the station itselfof the signal from mobile station 10 and transmits a request responsesignal containing information of the measured interference level and theinterstation communication speed determined at step S68 to mobilestation 10 (S70). Mobile station 10 determines the communication speedon the communication path of mobile station 10-relay station 30A-basestation 20, based on the request response signal transmitted from therelay station 30A (S72). Specifically, the mobile station firstdetermines the interstation communication speed between mobile station10 and relay station 30A on the basis of the interference level includedin the request response signal and then determines the communicationspeed on the communication path of mobile station 10-relay station30A-base station 20, based on the interstation communication speedbetween mobile station 10 and relay station 30A thus determined andbased on the interstation communication speed between relay station 30Aand base station 20 included in the request response signal.

Subsequently, the mobile station determines whether the determinedcommunication speed is greater than the communication speed by singlehop connection, and determines whether the communication path of mobilestation 10-relay station 30A-base station 20 should be selected (S74).When the communication speed is greater than that on the communicationpath by single hop connection, the communication path of mobile station10-relay station 30A-base station 20 is selected. When the communicationpath of mobile station 10-relay station 30A-base station 20 is selected,mobile station 10 transmits a connection notification to the relaystation 30 (S76). The relay station 30, receiving the connectionnotification from mobile station 10, further transmits a connectionnotification to base station 20 (S78); base station 20, receiving theconnection notification, transmits an ACK to the relay station 30A(S80); a communication is established between relay station 30A and basestation 20 (S82). Subsequently, after the establishment of thecommunication with base station 20, the relay station 30A transmits anACK to mobile station 10 (S84), and a communication is establishedbetween mobile station 10 and relay station 30A (S86). A method ofrealizing the communication at the determined communication speed may bea method of changing a modulation system or a method of changing aspreading system.

Subsequently, mobile station 10 again transmits a request signal (S88).The request signal transmitted on this occasion is a request signaltransmitted in order to search for a relay station 30B available formultihop communication. In order to search for a relay station 30B inthe neighborhood of mobile station 10, mobile station 10 transmits therequest signal by a transmission power necessary for transmission withina predetermined range. Mobile station 10 does not have to acknowledgethat relay stations 30A, 30B exist in the neighborhood, before thetransmission of the request signal. The mobile station firstacknowledges that relay stations 30A, 30B exist, by transmitting arequest signal and receiving a request response signal thereto. A relaystation 30B, receiving the request signal transmitted from mobilestation 10, transmits a request response signal to mobile station 10 inaccordance with the same flow as in the case of relay station 30A(S90-S96). Mobile station 10, receiving the request response signal fromthe relay station 30B, determines the communication speed on thecommunication path of mobile station 10-relay station 30B-base station20, based on the received request response signal (S98). Subsequently,mobile station 10 selects a communication path with a largercommunication speed out of the communication path with an intermediaryof relay station 30A connected before and the communication path with anintermediary of relay station 30B (S100). When the communication pathvia relay station 30B is selected herein, as shown in FIG. 16, acommunication is established on the communication path of mobile station10-relay station 30B-base station 20. Namely, mobile station 10transmits a connection notification to the relay station 30B (S102) andthe relay station 30B, receiving the connection notification, transmitsa connection notification to base station 20 (S104). Base station 20,receiving the connection notification, transmits an ACK to the relaystation 30B and a communication is established between relay station 30Band base station 20 (S108). Furthermore, the relay station 30B inestablishment of the communication with base station 20, transmits anACK to mobile station 10 (S110) and a communication is establishedbetween mobile station 10 and relay station 30B (S112). In this case,the communication path of mobile station 10-relay station 30A-basestation 20 is disconnected. Namely, the communication path via relaystation 30A is switched to the communication path via relay station 30B.Conversely, if the communication path via relay station 30A is selected,the communication is not established on the communication path via relaystation 30B, but the communication path of mobile station 10-relaystation 30A-base station 20 is maintained. The flow shown in FIG. 16ends here, but the operation for mobile station 10 to transmit therequest signal and search for the communication path with the largercommunication speed is repeated before the end of the communication withbase station 20. The communication path determined by this flow can beapplied, not only to the case where packets are transmitted from mobilestation 10 to base station 20, but also to the case where packets aretransmitted from base station 20 to mobile station 10. Namely, thepresent embodiment can also adapt to cases where bidirectionalcommunications are carried out through the communication path determinedby one station.

Although the present embodiment was configured so that mobile station 10functioned as a transmitting station and determined the communicationpath between mobile station 10 and base station 20, it is also possible,for example, to adopt a configuration wherein relay station 30Afunctions as a transmitting station and determines the communicationpath with the largest communication speed from relay station 30A to basestation 20. By adopting this configuration, the communication path withthe largest communication speed between relay station 30A and basestation 20 can be determined, after the communication path of mobilestation 10-relay station 30A-base station 20 is established.

In the present embodiment, the station having transmitted the requestsignal (mobile station 10 or relay station 30) determines theinterstation communication speed between the station and the station asa source of the request response signal, based on the interference levelat the station as a source of the request signal included in the requestresponse signal transmitted in response to the request signal. Anotherpotential configuration is that the station having received the requestsignal (relay station 30 or base station 20) determines the interstationcommunication speed between the station and the station as a source ofthe request signal, based on the interference level at the stationitself and the propagation loss of the request signal. When thisconfiguration is adopted, information about the determined interstationcommunication speed is put into the request response signal and therequest response signal is transmitted to the station as a source of therequest signal.

In the mobile communication system and communication path determiningmethod according to the second embodiment, first, mobile station 10establishes the single hop communication with base station 20,thereafter transmits the request signal to search for a multihopcommunication path, and determines the communication speed on thecommunication path found by the search, based on the request responsesignal. In this configuration, while the communication is firstestablished between mobile station 10 and base station 20, the selectionof the communication path can be carried out on the basis of thecommunication speeds to implement changeover to a communication pathwith a larger communication speed, whereby it is feasible to search fora communication path with higher quality (higher speed) while decreasingthe time period before establishment of communication.

Since the first established single hop communication path is alwaysmaintained, communication can be continuously carried out on the singlehop communication path even with a disconnection of the multihopconnection, whereby it is feasible to reduce the risk of disconnectionof communication. When the operation of searching for a multihopcommunication path and determining a communication path is again carriedout after the start of the communication on the single hop communicationpath as described above, it is also feasible to again switch over to acommunication path with a larger communication speed.

The above second embodiment described the case wherein mobile station(transmitting station) 10 was provided with communication pathdeterminer 11, determined the communication speed between thetransmitting station and the receiving station on the basis of therequest response signal transmitted from base station 20 or from relaystation 30, and determined the communication path on the basis thereof.It is also possible to adopt a configuration wherein base station(receiving station) 20 has the communication path determiner. Namely,when mobile station 10 or relay station 30 transmits a request signal,base station 20 determines the communication speeds on the respectivecommunication paths, based on the interference levels at the basestation itself and the relay information included in the request signal(the interstation communication speed information between each pair ofstations constituting the communication path between mobile station 10and base station 20), and determines the communication path on the basisthereof.

Third Embodiment

The following will describe programs to substantialize the mobilestation (transmitting station), relay station, and base station(receiving station) constituting the mobile communication systemaccording to the present invention. A computer to execute the programsaccording to the present embodiment is a terminal such as a cell phoneor the like forming the mobile communication system, and computer with acommunication function by mobile communication.

FIG. 17 are illustrations showing the configurations of thecommunication path control programs according to the third embodimentfor substantializing the mobile communication system in the firstembodiment. When the communication path control programs are applied tothe respective stations of the transmitting station, relay station, andreceiving station, they serve as a transmitting station program, as arelay station program, and as a receiving station program, respectively.FIG. 17A shows transmitting station program 110A, FIG. 17B relay stationprogram 130A, and FIG. 17C receiving station program 120A.

As shown in FIG. 17A, transmitting station program 110A is comprised ofcommunication path determining module 111 having request signaltransmitting module 111 a, request response signal receiving module 111b, and signal analyzing module 111 c. It is noted that the illustrationincludes only the components necessary for substantializing thecommunication path determining method according to the presentinvention, while omitting the other components. Request signaltransmitting module 111 a has a function of letting the computertransmit a request signal. Request response signal receiving module 111b has a function of letting the computer receive a request responsesignal. Signal analyzing module 111 c has a function of letting thecomputer analyze a request response signal and determine whether it ispossible to perform communication. The functions substantialized byletting the computer execute the request signal transmitting module 111a, request response signal receiving module 111 b, and signal analyzingmodule 111 c are the same as the functions of request signal transmitter11 a, request response signal receiver 11 b, and signal analyzer 11 c,respectively, of mobile station 10 in the first embodiment.

As shown in FIG. 17B, relay station program 130A has request signalreceiving module 131, request signal transmitting module 132, requestresponse signal receiving module 133, request response signaltransmitting module 134, interference level measuring module 136, andcommunication propriety determining module 137. Request signal receivingmodule 131 has a function of letting the computer receive a requestsignal. Request signal transmitting module 132 has a function of lettingthe computer transmit a request signal. Request response signalreceiving module 133 has a function of letting the computer receive arequest response signal. Request response signal transmitting module 134has a function of letting the computer transmit a request responsesignal. Interference level measuring module 136 has a function ofletting the computer measure an interference level. Communicationpropriety determining module 137 has a function of letting the computerdetermine the propriety of communication, based on the interferencelevel measured by the interference level measuring module. The functionssubstantialized by letting the computer execute the request signalreceiving module 131, request signal transmitting module 132, requestresponse signal receiving module 133, request response signaltransmitting module 134, interference level measuring module 136, andcommunication propriety determining module 137 are the same as thefunctions of request signal receiver 31, request signal transmitter 32,request response signal receiver 33, request response signal transmitter34, interference level measuring part 36, and communication proprietydeterminer 37, respectively, of relay station 30 in the firstembodiment.

As shown in FIG. 17C, receiving station program 120A has request signalreceiving module 121, interference level measuring module 122, requestresponse signal transmitting module 123, and communication proprietydetermining module 124. Request signal receiving module 121 has afunction of letting the computer receive a request signal. Interferencelevel measuring module 122 has a function of letting the computermeasure an interference level. Request response signal transmittingmodule 123 has a function of letting the computer transmit a requestresponse signal. Communication propriety determining module 124 has afunction of letting the computer determine the propriety ofcommunication on the basis of the interference level measured byinterference level measuring module 122. The functions substantializedby letting the computer execute the request signal receiving module 121,interference level measuring module 122, request response signaltransmitting module 123, and communication propriety determining module124 are the same as the functions of request signal receiver 121,interference level measuring part 122, request response signaltransmitter 123, and communication propriety determiner 124,respectively, of base station 20 in the first embodiment.

Fourth Embodiment

Communication path control programs according to the fourth embodimentfor substantializing the mobile communication system in the secondembodiment will be described below with reference to FIG. 18. FIG. 18Ais an illustration showing the configuration of transmitting stationprogram 110B, the configuration of relay station program 130B, and theconfiguration of receiving station program 120B.

As shown in FIG. 18A, transmitting station program 110B according to thefourth embodiment is identical in the basic configuration to thetransmitting station program 110A according to the third embodiment, butis different therefrom in that it is provided with communication speeddetermining module 111 d in place of signal analyzing module 111 c.Communication speed determining module 111 b has interstationcommunication speed determining module 111 e for letting the computerdetermine the interstation communication speed between the transmittingstation and a station as a source of a request response signal.Communication speed determining module 111 d has a function of lettingthe computer determine the communication speed between the transmittingstation and the receiving station, based on the interstationcommunication speed determined by interstation communication speeddetermining module 111 e, and the interstation communication speedbetween each pair of stations constituting a communication path,included in a request response signal received by the request responsesignal receiving module. The function substantialized by letting thecomputer execute the communication speed determining module 111 d is thesame as the function of communication speed determiner 11 d of mobilestation 10 in the second embodiment.

As shown in FIG. 18B, relay station program 130B according to the fourthembodiment is identical in the basic configuration to the relay stationprogram 130A according to the third embodiment, but is differenttherefrom in that it is provided with interstation communication speeddetermining module 138 in place of communication propriety determiningmodule 137. Interstation communication speed determining module 138 hasa function of letting the computer determine the communication speed tothe receiving station, based on the interference level included in therequest response signal. The function substantialized by letting thecomputer execute the interstation communication speed determining module138 is the same as the function of interstation communication speeddeterminer 38 of relay station 30 in the second embodiment.

As shown in FIG. 18C, receiving station program 120B according to thefourth embodiment is identical in the basic configuration to thereceiving station program 120A according to the third embodiment, but isdifferent therefrom in that it does not have communication proprietydetermining module 126. The functions substantialized by letting thecomputer execute the receiving station program 120B according to thefourth embodiment are the same as those of base station 20 according tothe second embodiment.

The following will describe a receiving station program forsubstantializing the receiving station with the communication pathdeterminer for determining the communication path. FIG. 19 is anillustration showing the configuration of the receiving station program.As shown in FIG. 19, the receiving station program is comprised of acommunication path determining module having request signal receivingmodule 121, interference level measuring module 122, communication speeddetermining module 123, and communication path selecting module 124.Request signal receiving module 121 has a function of letting thecomputer receive a request signal. Interference level measuring module122 has a function of letting the computer measure an interference levelof a request signal received by the computer. Communication speeddetermining module 124 has interstation communication speed determiningmodule 124 a. Interstation communication speed determining module 124 ahas a function of letting the computer determine the interstationcommunication speed, based on the interference level, and communicationspeed determining module 124 has a function of letting the computerdetermine a communication speed between the transmitting station and thereceiving station, based on an interstation communication speed betweeneach pair of stations constituting a communication path. Communicationpath selecting module 125 has a function of letting the computer selecta communication path on the basis of communication speeds on respectivecommunication paths. The receiving station program may also beconfigured to have communication path information transmitting module129 for letting the computer transmit the information of the selectedcommunication path, as indicated by a dotted line in FIG. 19. In thisconfiguration, the information of the determined communication path istransmitted to the transmitting station and the transmitting stationtransmits packets according to the determined communication path.

The above described the mobile communication systems and communicationpath determining methods according to the present invention with theembodiments thereof, but it is noted that the present invention is by nomeans intended to be limited to the above embodiments.

For example, the above second embodiment described the configurationwherein each relay station 30 had the interstation communication speeddetermining means, determined the interstation communication speed onthe basis of the interference level, and transmitted the interstationcommunication speed information to mobile station 10, but anotherpotential configuration is such that each relay station 30 and basestation 20 are configured to put the interference level measured by theinterference level measuring part, into a request response signal andtransmit the request response signal to mobile station 10. In thisconfiguration, mobile station 10 is able to determine the interstationcommunication speed information between each pair of stations, based onthe interference levels at the respective stations, and mobile station10 is able to determine the communication speed between mobile station10 and base station 20, based on the determined interstationcommunication speeds, and to determine the communication path.Conversely, the interference level at each relay station 30 may be putinto a request signal to be transmitted to base station 20. This permitsbase station 20 to determine the interstation communication speedinformation between each pair of stations, based on the interferencelevels at the respective stations, and the base station 20 is able todetermine the communication speed between the mobile station 10 and basestation 20, based on the determined interstation communication speeds,and determine the communication path.

Fifth Embodiment

According to each of the above embodiments, it is feasible to determinethe communication path with the largest (highest) communication speed orthe communication path satisfying the predetermined line quality (thesecommunication paths will be referred to as “optimal path”), based on theinterference levels of the respective signals received at the relaystation and at the receiving station. In the present embodiment, theoptimal path is determined so as to secure the reception quality fromthe mobile station to the base station in the following manner.

In the CDMA mobile communication system, a parameter E determined by aratio of required reception power per bit as a target at the receivingstation (E_(b)) to thermal noise (N₀) plus interference power (I₀) i.e.,E=E _(b)/(N ₀ +I ₀),is a factor to determine the reception quality of signal in control oftransmission power. Using this parameter E as a target value oftransmission power control, the probability of erroneous reception ofsignal (error rate) decreases with increase of this target value, but itbrings about the disadvantage of decrease in the cell radius and systemcapacity. For this reason, in the conventional CDMA mobile communicationsystem, the target value is set to the minimum necessary value tocontrol the transmission power, so as to secure the reception quality ofsignal at the base station.

However, since the multihop connection system involves the communicationwith the base station through relay stations, in order for the basestation to receive correct signals, the base station and all the relaystations have to receive the signals without error. Therefore, in orderto realize the error rate in the multihop connection system equivalentto that in the conventional system (single hop system), the target valuemust be set large, so as to achieve a small error rate at each station.However, the increase of the target value would result in decreasing thecell radius and system capacity.

Taking this point in account, the present embodiment adopts thefollowing configuration to enhance the reception quality, i.e., decreasethe error rate, while minimizing the decrease of the cell radius andsystem capacity. The description hereinafter will be given with focus ondifferences from each of the above embodiments, with omission andsimplification of the description of common portions.

The mobile communication system in the present embodiment is configuredto set the target value for transmission power control, and the targetvalue is independently (uniquely) set for each of the case where thebase station is a receiving station and the case where the relay stationis a receiving station. Namely, a base-station target value is uniquelycalculated at the base station in accordance with a condition specificto the base station, and a relay-station target value is uniquelycalculated at the relay station in accordance with a condition specificto the relay station. Then the target value at the base station(hereinafter referred to as “base-station target value”) is set to theminimum necessary value permitted, while the target value at the relaystation (hereinafter referred to as “relay-station target value”) is setas a value different from and larger than the base-station target value.

The mobile communication system in the present embodiment will bedescribed below in detail.

Mobile communication system 1 in the present embodiment has the systemconfiguration shown in FIG. 1, similar to that of mobile communicationsystem 1 in the first embodiment. The mobile station has the sameconfiguration shown in FIG. 3, as the mobile station 10. The presentembodiment is different in base station 20 and relay station 30 from thefirst embodiment.

Relay station 30 in the present embodiment has an internal configurationsimilar to that of relay station 30 in the first embodiment. It isdifferent from relay station 30 in the first embodiment in thatcommunication propriety determiner 37 has a target value storage forstoring a preliminarily calculated target value for transmission powercontrol and this target value storage stores the relay-station targetvalue.

The relay-station target value is calculated so as to define the numberof relays permitted and make the error rates at base station 20 and ateach relay station 30 satisfy Formula 1 below, independently of theafter-described base-station target value at base station 20.

The relay-station target value at each relay station 30 may be setindependently of the base-station target value at base station 20 andthe relay-station target values at respective relay stations 30 may beset in similar fashion. However, the relay-station target values at therespective relay stations 30 may be set to different values according totheir respective circumstances, such as installation environments of therespective relay stations 30 or the like, as occasion may demand.

Here the aforementioned parameter E can be used as the relay-stationtarget value, for example. Other potential factors include SIR (Signalto Interference Ratio: ratio of signal power to interference power), CIR(Carrier Interference Ratio: ratio of carrier power to interferencepower), and a reception level.1−(total error rate)>(1−(error rate at base station))×(1−(error rate atrelay station))^(x)  Formula 1

x: number of relays

Then communication propriety determiner 37 determines whether it ispossible to perform the communication at the communication speedrequested by the request signal received by request signal receiver 31,based on the interference level measured by interference level measuringpart 36 and the relay-station target value stored. For example,communication propriety determiner 37 determines a maximum communicationspeed available for communication and compatible with the relay-stationtarget value, based on the interference level measured by interferencelevel measuring part 36, and compares the maximum communication speedwith the requested communication speed. Then the result of thedetermination by communication propriety determiner 37 is fed intorequest response signal transmitter 34 and the operation thereafter ismuch the same as in the first embodiment.

Base station 20 in the present embodiment has the internal configurationsimilar to that of base station 20 in the first embodiment. It isdifferent from base station 20 in the first embodiment in thatcommunication propriety determiner 26 has a target value storage forstoring a preliminarily calculated target value for transmission powercontrol and the target value storage stores the base-station targetvalue.

Here the base-station target value is calculated so as to satisfy aboveFormula 1 in a manner similar to the relay-station target value andindependently of the relay-station target value and, for example, it isselected from the aforementioned parameter E, SIR, CIR, and receptionlevel.

Then communication propriety determiner 26 determines whether it ispossible to perform the communication with mobile station 10, based onthe interference level measured by interference level measuring part 22and the base-station target value stored. For example, thisdetermination is made as follows: the communication propriety determinerdetermines a maximum communication speed available for communication andcompatible with the base-station target value, based on the interferencelevel measured by interference level measuring part 22 and compares themaximum communication speed with the communication speed requested bythe request signal. Then request response signal transmitter 23transmits a request response signal containing the communicationpropriety information on propriety based on the determination bycommunication propriety determiner 26 to relay station 30 or mobilestation 10 as a source. The operation thereafter is similar to that inthe first embodiment.

The communication path determining methods in the present embodimentinclude methods of determining the communication path with the largestcommunication speed (hereinafter referred to as “fastest pathdetermining methods”) and methods of determining the communication pathsatisfying the required line quality (hereinafter referred to as“required quality path determining methods”). These methods will bedescribed with examples where mobile station 10 is a transmittingstation, with focus on differences from the communication pathdetermining methods in the first embodiment. Common description will beomitted or simplified.

A fastest path determining method is carried out according to theprocedure shown in FIG. 8, as in the case of the first embodiment. Thefollowing is the procedure in a case where the search is sequentiallyconducted staring from the path with the maximum communication speed(hereinafter referred to as “descending sequence search”).

First, as in the first embodiment, mobile station 10 attempts to connectby 384 kbps single hop connection (S11) and determines whether it ispossible to perform communication by 384 kbps single hop connection. Atthis time, signal analyzer 11 c analyzes the communication proprietyinformation included in the request response signal. When it isimpossible to perform the communication by 384 kbps single hopconnection, mobile station 10 searches for a relay station 30 capable ofcommunication by 384 kbps multihop connection (S12). At this time,mobile station 10 transmits a request signal to relay station 30. Then arelay station 30 receives the request signal and measures theinterference level at the relay station itself. The relay station 30makes communication propriety determiner 37 determine whether it ispossible to perform the communication at the communication speedrequested by the request signal (384 kbps herein), based on the measuredinterference level and the relay-station target value stored.

Then information indicating the result of this determination istransmitted to mobile station 10 or to base station 20 in much the samemanner as in the first embodiment.

When communication propriety determiner 37 determines that it ispossible to perform the communication, the relay station 30 transmits arequest signal to base station 20. Base station 20, receiving therequest signal, measures the interference level at the station itself.Base station 20 makes communication propriety determiner 26 determinewhether it is possible to perform the communication with mobile station10 at the requested communication speed, based on the measuredinterference level and the stored base-station target value. Then basestation 20 transmits a request response signal similar to that in thefirst embodiment, to the relay station 30. When the relay station 30receives the request response signal, it transmits a request responsesignal containing the communication propriety information included inthe request response signal, and the communication propriety informationat the relay station itself (“communicable” herein). Mobile station 10makes signal analyzer 11 c analyze the communication proprietyinformation included in the received request response signal. When theresult of the analysis is that it is possible to perform thecommunication by 384 kbps multihop connection, the mobile stationdetermines the communication path by 384 kbps multihop connection andstarts the communication.

On the other hand, when it is impossible to perform the communication by384 kbps multihop connection, mobile station 10 attempts to connect by64 kbps single hop connection (S13). This is much the same as theattempt on 384 kbps single hop connection in the present embodiment asdescribed above. When it is possible herein to perform the communicationby 64 kbps single hop connection, the mobile station determines thecommunication path by 64 kbps single hop connection and starts thecommunication. When it is impossible to perform the communication by 64kbps single hop connection, mobile station 10 attempts to connect by 64kbps multihop connection (S14). This is much the same as the attempt on384 kbps multihop connection in the present embodiment as describedabove.

In the case of the descending sequence search, as described above,mobile station 10 sequentially attempts to connect from the fastestcommunication speed and establishes a connection with base station 20 ata communication speed determined as communicable, thereby determiningthe communication path with the largest communication speed. Inaddition, in the case of the present embodiment, the communication pathwith the largest communication speed is determined based on therelay-station target value and the base-station target value calculatedindependently of each other at relay station 30 and at base station 20,and it is thus feasible to enhance the reception quality whileminimizing the decrease of the cell radius and system capacity.

The procedure in a case where the search is sequentially conductedstarting from the path with the minimum communication speed (hereinafterreferred to as “ascending sequence search”) is as shown in FIG. 9. Inthis case, first, mobile station 10 attempts to connect by 64 kbpsmultihop connection (S21). At this time, in a manner similar to theaforementioned attempt on 384 kbps multihop connection, relay station 30and base station 20 each make communication propriety determiner 37 andcommunication propriety determiner 26 determine whether it is possibleto perform the communication at the requested communication speed, basedon the interference level at each station and the relay-station targetvalue or the base-station target value.

Then, for example, while maintaining the 64 kbps multihop connection, asin the first embodiment, the mobile station attempts to connect by 64kbps single hop connection (S22 or S23). Then mobile station 10 attemptsto connect by 384 kbps multihop connection (S24). In this case, relaystation 30 and base station 20 each also make their respectivecommunication propriety determiner 37 and communication proprietydeterminer 26 determine whether it is possible to perform thecommunication at the requested communication speed, based on theinterference level and the relay-station target value or thebase-station target value stored. Then, for example, while maintainingthe 64 kbps multihop connection, as in the first embodiment, the mobilestation attempts to connect by 384 kbps single hop connection (S25 orS26).

In the case of the ascending sequence search, as described above, thecommunication path is first secured to keep the time before the start ofcommunication as short as possible, and the communication path with thelargest communication speed is searching for, while stepwise increasingthe communication speed. In that case, the communication path isdetermined on the basis of the interference level at each station andthe relay-station target value and the base-station target valuecalculated independently of each other at relay station 30 and at basestation 20, whereby the reception quality can be enhanced, whileminimizing the decrease of the cell radius and system capacity.

The required quality path determining methods will be described below.In the present embodiment, the required quality path determining methodsalso involve applications to both the first multihop system shown inFIG. 10A and the second multihop system shown in FIG. 10B. The requiredquality path determining method in the former multihop system is carriedout according to the procedure shown in FIG. 11, as in the firstembodiment.

First, when the required line quality is given by a communication speed(S30), mobile station 10 attempts to make a single hop connection at thecommunication speed (S31, S33, S35, or S37). At this time, mobilestation 10 first transmits a request signal at the given communicationspeed, as in the first embodiment. Base station 20 receives the requestsignal transmitted from mobile station 10 and measures the interferencelevel at the base station itself. Then communication proprietydeterminer 26 determines whether it is possible to perform thecommunication with mobile station 10 at the communication speedrequested by the request signal, based on the measured interferencelevel and the stored base-station target value. Then base station 20puts the communication propriety information based on the determinationinto a request response signal and transmits the request response signalto mobile station 10. Mobile station 10, receiving the request responsesignal, determines whether it is possible to perform the single hopcommunication at the given communication speed, based on thecommunication propriety information included therein. When it ispossible herein to perform the single hop communication, the mobilestation determines the communication path thereof and starts thecommunication. However, if it is impossible, the mobile station attemptsto make a multihop connection at the communication speed of twice thecommunication speed (double speed) (S32, S34, or S36). At this time,mobile station 10 transmits a request signal containing a communicationconnection request at the double speed. A relay station 30, receivingthe request signal, measures the interference level at the relay stationitself. The relay station 30 also makes communication proprietydeterminer 37 determine whether it is possible to perform thecommunication at the communication speed requested by the requestsignal, based on the measured interference level and the storedrelay-station target value. When the result of the determination is thatit is impossible to perform the communication, the relay station 30transmits a request response signal containing the communicationpropriety information to the mobile station; when it is possible toperform the communication, the relay station 30 transmits a requestsignal containing a communication connection request at the doublespeed.

When base station 20 receives the request signal, it measures theinterference level at the base station itself and makes communicationpropriety determiner 26 determine whether it is possible to perform thecommunication with mobile station 10 at the requested communicationspeed, based on the interference level and the base-station targetvalue. The operation thereafter is similar to that in the firstembodiment.

The required quality path determining method in the latter multihopsystem is carried out according to the procedure shown in FIG. 12, as inthe first embodiment.

First, when the required line quality is given by a communication speed,mobile station 10 attempts to make a single hop connection at thecommunication speed (S41, S43, S45, or S47). A specific method of theattempt on connection is just as described above. When it is possibleherein to perform the communication at the given communication speed,the mobile station determines the communication path of the single hopconnection at the communication speed and starts the communication.However, if it is impossible, the mobile station attempts to make amultihop connection at the communication speed (S42, S44, S46, or S48).In this case, a specific method of the attempt on connection is just asdescribed above.

When it is possible to perform the multihop communication at thecommunication speed requested by the request signal, the mobile stationdetermines the communication path of the multihop connection at thecommunication speed and starts the communication.

As described above, the present embodiment is also configured so thatwith a requested line quality being given, it is feasible to determinethe communication path satisfying the line quality and make aconnection, and, therefore, it can provide a high-quality communicationenvironment. Since the communication path is determined based on therelay-station target value and the base-station target value calculatedindependently of each other at relay station 30 and at base station 20,it is feasible to enhance the reception quality while minimizing thedecrease of the cell radius and system capacity.

Sixth Embodiment

The present embodiment is configured as described below, in order todetermine the optimal communication speed so as to secure the receptionquality from the mobile station to the base station in the secondembodiment.

In mobile communication system 1 according to the present embodiment,the target values for transmission power control are also independently(individually) set in the case where the base station is a receivingstation and in the case where the relay station is a receiving station.The base-station target value is set to the minimum necessary valuepermitted, and the relay-station target value is set larger than it.

Mobile communication system 1 according to the present embodiment hasthe system configuration similar to the mobile communication system inthe second embodiment. The base station also has the same configurationas the base station 20 shown in FIG. 15. The mobile communication systemof the present embodiment is different in mobile station 10 and relaystation 30 from the mobile communication system in the secondembodiment.

In the present embodiment mobile station 10 has the internalconfiguration similar to mobile station 10 in the second embodiment. Themobile station 10 in the present embodiment is different from mobilestation 10 in the second embodiment in that interstation communicationspeed determiner lie has a target value storage for storingpreliminarily calculated target values for transmission power control.

The target value storage stores the base-station target value andrelay-station target value similar to those in the fifth embodiment.These base-station target value and relay-station target value areindependently calculated so as to satisfy aforementioned Formula 1 as inthe fifth embodiment. The both target values can be selected from theaforementioned parameter E, SIR, CIR, and reception level.

Then interstation communication speed determiner 11 e determines theinterstation communication speed between the mobile station and relaystation 30 or base station 20 as a source of a request response signal,based on the interference level at the source of the request responsesignal included in the request response signal and based on thebase-station target value and relay-station target value stored.

In the present embodiment relay station 30 has the internalconfiguration similar to relay station 30 in the second embodiment. Therelay station in the present embodiment is different from relay station30 in the second embodiment in that interstation communication speeddeterminer 38 has a target value storage for storing a preliminarilycalculated target value for transmission power control.

The target value storage stores the relay-station target value. Therelay-station target value is calculated independently of thebase-station target value stored in mobile station 10, so as to satisfyaforementioned Formula 1. The relay-station target value can be selectedfrom the aforementioned parameter E, SIR, CIR, and reception level.

Interstation communication speed determiner 38 determines theinterstation communication speed between the host relay station andrelay station 30 or base station 20 as a source of a request responsesignal, based on the interference level included in the request responsesignal received by request response signal receiver 33, and based on therelay-station target value stored.

The communication path determining method in mobile communication system1 according to the present embodiment will be described below. Thiscommunication path determining method is carried out according to theflowchart shown in FIG. 16, as in the second embodiment, and thedescription hereinafter will be given with focus on the differences fromthe second embodiment, with omission and simplification of commonportions.

After the steps S50 and S52 are executed in a manner similar to those inthe second embodiment, mobile station 10 receives a request responsesignal transmitted from base station 20, and then operates as follows.Namely, mobile station 10 determines a communication speed, based on therequest response signal received and based on the base-station targetvalue and relay-station target value stored (S54), and transmits aconnection notification containing the information of the determinedcommunication speed to base station 20 (S56). When base station 20receives this connection notification, it sends an ACK to mobile station10 (S58). Then a single hop communication is established between mobilestation 10 and base station 20 (S60). This single hop communication isalways maintained before an end of the communication between mobilestation 10 and base station 20.

After the steps S62, S64, and S66 are then executed in a manner similarto those in the second embodiment, the relay station 30A receives arequest response signal transmitted from base station 20, and thendetermines the interstation communication speed between the relaystation and base station 20, based on the interference level included inthe request response signal and based on the relay-station target valuestored (S68). The relay station 30A also transmits a request responsesignal containing information about the interference level at the relaystation itself and about the interstation communication speed determinedat step 68 to mobile station 10. Mobile station 10 determines thecommunication speed on the communication path of mobile station 10-relaystation 30A-base station 20, based on the request response signaltransmitted from the relay station 30A and on the base-station targetvalue and relay-station target value stored (S72). Specifically, theoperation is carried out as follows. First, the mobile stationdetermines the interstation communication speed between mobile station10 and relay station 30A, based on the interference level at relaystation 30A included in the request response signal and therelay-station target value stored. Then the mobile station determinesthe communication speed on the communication path of mobile station10-relay station 30A-base station 20, based on the interstationcommunication speed between mobile station 10 and relay station 30A thusdetermined, the interstation communication speed between relay station30A and base station 20 included in the request response signal, and thebase-station target value.

Subsequently, the steps of S74 to S86 are carried out in similar fashionto those in the second embodiment and thereafter mobile station 10 againtransmits a request signal, in order to search for a relay station 30B.Then the relay station 30B transmits a request response signal to mobilestation 10 in the same procedure as in the case of relay station 30A(S88-S96). Mobile station 10, receiving the request response signal fromrelay station 30B, determines the communication speed on thecommunication path of mobile station 10-relay station 30B-base station20, based on the received request response signal and the base-stationtarget value and relay-station target value stored (S98). The operationthereafter is carried out by executing the steps similar to those in thesecond embodiment.

In the present embodiment, as described above, mobile station 10determines the interstation communication speed on the basis of theinterference level and the relay-station target value and base-stationtarget value calculated independently, and relay station 30 determinesthe interstation communication speed on the basis of the interferencelevel and the relay-station target value. Therefore, the presentembodiment permits the optimal path to be determined based on thecommunication speeds between each pair of stations, and the receptionquality can be enhanced while minimizing the decrease of the cell radiusand system capacity.

Incidentally, as described above, mobile communication system 1 in eachof the fifth and sixth embodiments is configured to set the targetvalues for the error rates at all the stations (base station 20 and eachrelay station 30) on the communication path, instead of the error rateat base station 20, and to determine the optimal path on the basis ofthe target values. This makes it feasible to secure the receptionquality from the mobile station to the base station even in the multihopconnection system.

According to “W-CDMA Mobile Communications System” (published under thegeneral editorship of Keiji Tachikawa by Maruzen Co., Ltd.) and others,the system capacity C and parameter E have the relation of Formula 2below.C=(pg/E)+1  Formula 2

pg: spreading gain

Namely, the value of system capacity C decreases with increase of theparameter E. An increase of parameter E at relay station 30 will resultin increase of interference and thus decrease of system capacity, butthe effect on the system capacity is less than the effect due to theincrease of parameter E at base station 20. Noting this point, mobilecommunication system 1 in the present embodiment is configured to setthe base-station target value to the minimum necessary value permittedand set the relay-station target value larger than it, whereby thedecrease of system capacity is suppressed while keeping the error ratesmall in the entire system.

The following will describe programs to substantialize the mobilestation (transmitting station), relay station, and base station(receiving station) constituting the mobile communication systemsaccording to the fifth embodiment and the sixth embodiment. The programsfor substantializing the respective stations constituting the mobilecommunication system in the fifth embodiment have the modules common tothe aforementioned programs, and the description hereinafter will begiven with focus on different modules, with omission and simplificationof the description about the common modules.

The programs for the respective stations constituting mobilecommunication system 1 in the fifth embodiment have the configurationsshown in FIG. 17 as the programs in the third embodiment did. Among theprograms, the transmitting station program is similar to thetransmitting station program 110A according to the third embodimentshown in FIG. 17A. The relay station program and the receiving stationprogram have the same modules as the relay station program 130A and thereceiving station program 120A, respectively, according to the thirdembodiment as shown in FIGS. 17B and 17C, except for the communicationpropriety determining modules 137, 124.

Communication propriety determining module 137 has a function of lettingthe computer determine the propriety of communication, based on theinterference level measured by the interference level measuring moduleand on the relay-station target value. Communication proprietydetermining module 124 has a function of letting the computer determinethe propriety of communication, based on the interference level measuredby interference level measuring module 122 and on the base-stationtarget value.

The programs for the respective stations constituting mobilecommunication system 1 according to the sixth embodiment have theconfigurations shown in FIG. 18 as the programs according to the fourthembodiment did. Among the programs, the receiving station program issimilar to the receiving station program 120B according to the fourthembodiment shown in FIG. 18C. The transmitting station program and therelay station program have the same modules as the transmitting stationprogram 110B and the relay station program 130B, respectively, in thefourth embodiment as shown in FIGS. 18A and 18B, except for theinterstation communication speed determining module 111 e and theinterstation communication speed determining module 138.

Interstation communication speed determining module 111 e has a functionof letting the computer determine the interstation communication speedbetween the transmitting station and the station as a source of arequest response signal, based on the interference level and on thebase-station target value and relay-station target value. Interstationcommunication speed determining module 138 has a function of letting thecomputer determine the communication speed to the receiving station,based on the interference level included in a request response signaland on the relay-station target value.

These programs enable the computer to substantialize the functions ofbase station 20, relay station 30, and mobile station 10 according toeach of the fifth and sixth embodiments described above. In that case,the reception quality can be enhanced while minimizing the decrease ofthe cell radius and system capacity.

Finally, a receiving station program to substantialize the receivingstation with the communication path determiner for determining thecommunication path will be described. This receiving station program hasthe configuration shown in FIG. 19, as the aforementioned receivingstation program 120 c did. This receiving station program has the samemodules as the receiving station program 120 c, except for theinterstation communication speed determining module 124 a. Theinterstation communication speed determining module 124 a has a functionof letting the computer determine the interstation communication speed,based on the interference level and the base-station target value. Thisreceiving station program enables the computer to substantialize theaforementioned functions of base station 20. In that case, the receptionquality can be enhanced while minimizing the decrease of the cell radiusand system capacity.

The fifth and sixth embodiments were described using the examples of“uplink” to connect mobile station 10 through relay station 30 to basestation 20. However, the fifth and sixth embodiments can also be appliedto “downlink,” by properly modifying the way of setting the systemcapacity and target values.

INDUSTRIAL APPLICABILITY

As described above, the present invention has realized suchdetermination of multihop or single hop communication path as todetermine the communication path with the largest (highest)communication speed or the communication path satisfying thepredetermined line quality, based on the interference levels of therespective signals received at the relay station constituting thecommunication path and at the receiving station, thereby achievingimplementation of fast communication.

1. A receiving station applied to a mobile communication system andconfigured to receive a packet from a transmitting station through acommunication path with an intermediary of at least one relay station orthrough a communication path without an intermediary of a relay station,the receiving station comprising: communication path determining meansfor determining a communication path with a largest communication speedor a communication path satisfying a required communication speed basedon interference levels of respective signals received at a relay stationand at the receiving station, the relay station constituting acommunication path between the transmitting station and the receivingstation.
 2. The receiving station according to claim 1, wherein thecommunication path determining means comprises: request signal receivingmeans for receiving a request signal transmitted from the transmittingstation or from the relay station; interference level measuring meansfor measuring an interference level at the receiving station when therequest signal receiving means receives a request signal; interstationcommunication speed determining means for determining an interstationcommunication speed between the receiving station and the transmittingstation or the relay station as a source of the request signal, based onthe interference level measured by the interference level measuringmeans; communication speed determining means for determining acommunication speed between the transmitting station and the receivingstation, based on the interstation communication speed determined by theinterstation communication speed determining means and, where therequest signal is one received from the relay station, also based oninterstation communication speed information between each pair ofstations constituting a communication path from the transmitting stationto said relay station, included in the request signal; and communicationpath selecting means for selecting a communication path, based oncommunication speeds on respective communication paths determined by thecommunication speed determining means.
 3. The receiving stationaccording to claim 1, wherein the communication path determining meanscomprises: request signal receiving means for receiving a request signaltransmitted from the transmitting station or from the relay station;interference level measuring means for measuring an interference levelat the receiving station when the request signal receiving meansreceives a request signal; interstation communication speed determiningmeans for determining an interstation communication speed between eachpair of stations constituting a communication path, based on theinterference level measured by the interference level measuring meansand, where the request signal is one transmitted from the relay station,also based on an interference level included in the request signal;communication speed determining means for determining a communicationspeed between the transmitting station and the receiving station on thebasis of the interstation communication speed determined by theinterstation communication speed determining means; and communicationpath selecting means for selecting a communication path, based oncommunication speeds on respective communication paths determined by thecommunication speed determining means.
 4. A receiving stationcomprising: request signal receiving means for receiving a requestsignal transmitted from a transmitting station through a communicationpath with an intermediary of at least one relay station or through acommunication path without an intermediary of a relay station, therequest signal including a required communication speed; interferencelevel measuring means for measuring an interference level at thereceiving station when the request signal receiving means receives arequest signal; communication propriety determining means fordetermining whether it is possible to perform communication at therequired communication speed included in the request signal, based onthe interference level measured by the interference level measuringmeans; and request response signal transmitting means for transmitting arequest response signal containing information on propriety ofcommunication determined by the communication propriety determiningmeans, through the communication path to the transmitting station. 5.The receiving station according to claim 4, wherein the communicationpropriety determining means memorizes a receiving-station target valuefor control of transmission power set independently of the relaystation, and determines whether it is possible to perform thecommunication at the communication speed included in the request signal,based on the interference level and the receiving-station target value.6. A receiving station comprising: request signal receiving means forreceiving a request signal transmitted from the transmitting station orfrom a relay station; interference level measuring means for measuringan interference level at the receiving station when the request signalreceiving means receives a request signal; interstation communicationspeed determining means for determining an interstation communicationspeed between the receiving station and the transmitting station or therelay station as a source of the request signal, based on theinterference level measured by the interference level measuring means;and request response signal transmitting means for transmitting arequest response signal containing the interstation communication speedinformation determined by the interstation communication speeddetermining means, to the transmitting station or the relay station as asource of the request signal.
 7. A receiving station applied to a mobilecommunication system and configured to receive a packet from atransmitting station through a communication path with an intermediaryof at least one relay station or through a communication path without anintermediary of a relay station, the receiving station comprising: acommunication path determining unit configured to determine acommunication path with a largest communication speed or a communicationpath satisfying a required communication speed, based on interferencelevels of respective signals received at a relay station and at thereceiving station, the relay station constituting a communication pathbetween the transmitting station and the receiving station.
 8. Areceiving station comprising: a request signal receiver configured toreceive a request signal transmitted from a transmitting station througha communication path with an intermediary of at least one relay stationor through a communication path without an intermediary of a relaystation, the request signal including a required communication speed; aninterference level measuring unit configured to measure an interferencelevel at the receiving station when the request signal receiver receivesa request signal; a communication propriety determining unit configuredto determine whether it is possible to perform communication at therequired communication speed included in the request signal, based onthe interference level measured by the interference level measuringunit; and a request response signal transmitter configured to transmit arequest response signal containing information on propriety ofcommunication determined by the communication propriety determiningunit, through the communication path to the transmitting station.
 9. Areceiving station comprising: a request signal receiver configured toreceive a request signal transmitted from the transmitting station orfrom a relay station; an interference level measuring unit configured tomeasure an interference level at the receiving station when the requestsignal receiver receives a request signal; an interstation communicationspeed determining unit configured to determine an interstationcommunication speed between the receiving station and the transmittingstation or the relay station as a source of the request signal, based onthe interference level measured by the interference level measuringunit; and a request response signal transmitter configured to transmit arequest response signal containing the interstation communication speedinformation determined by the interstation communication speeddetermining unit, to the transmitting station or the relay station as asource of the request signal.